Hello and welcome to my User Tip
Best way to uninstall programs or apps
The best way is to contact the developers site for uninstall instructions, especially if the software required you to enter your Admin password to install.
It might have placed "hooks" into the OS X kernel called kext files that load when OS X boots up or in other locations that require a uninstaller to use root level power to uninstall correctly.
If one simply only drags the application icon they see in their Applications or Utilities folder to the Trash, what happens is these leftover parts in OS X itself don't get updated for compatibility with later OS X updates and/or might cause a security or stability issue later on which the machine will boot to a "Gray Screen Issue" and remain stuck.
Self contained programs/apps
If the developer then says it's perfectly fine to drag the application icon located in the Applications or Applications > Utilities folder to the Trash, then you can do that. These types of programs are what we call "self contained" meaning everything it pretty much requires is inside the Application icon which is really a hidden folder called a "package".
Since "self contained" programs or apps can be run from just about anywhere they are placed, like in User Account folders so only that User can run them, however for global use amongst all User Accounts on the machine and in most cases of installers, they are stored in the Applications and/or Applications > Utilities folder.
Keep your Downloads folder clear
It is not advised to keep downloaded programs in the Downloads folder, rather to keep this clear at all times except during a known active download as to be wary of bad websites that will cause a "driveby download" hoping one will click or run to infect their machine. The Downloads folder is not a storage place, rather if you wish to keep a installer, place it someplace else in your User folders, like creating a folder called "Installers" or "Downloaded PDFs" and keeping them in your Utilities or Documents folders in your Home directory.
Concerning appdelete/appremoval type software
It is not advised to use "appdelete" type programs for the fact that there are hundreds of thousands of programs/apps and developers changing them all the time, thus it's almost impossible to keep up with all the changes. So as a result many of these appdelete type programs rely upon using a search feature and hoping the developer tagged their files with a name to locate files, which is not always the case. Accidents occur as users of these type programs delete other files or not get all parts installed by the developer.
Many developers use other developers software, like Pace for copy protection or Soundflower for a audio driver, when they install their software, thus the appdelete type software misses these files installed in the OS X kernel which then later get outdated or have security issues that are not fixed as the parent program is missing that does the updates.
Installing programs or apps
When you click a link on a website to download, it appears in your Downloads folder which you open that and then the DMG volume that appears on the Desktop (if it has one) and doublelclick the installer (if it says it is) or drag the self contained program to your Applications or Applications > Utilities folder.
Then from there you drag it's icon to the Dock to make a "Alias" or shortcut so you don't have to dig inside the Applications folder to find it. Click on the Dock Alias to launch the program.
Installers are not usually kept on the Dock, rather once the program is installed the Installer is either Trashed or saved someplace else out of the Downloads folder to keep it clear to watch for malicous downloads. Rather the program installed is kept a Alias in the Dock as that's what is going to be used, not the one time installer package.
For OS X 10.8 "Mountain Lion" users and above, Apple installed restrictions on where you can download and install software onto your machine. So if you go to a website and see something you like to install, Apple will prevent you from running the program and/or installer. The default security settings in your System Preferences > Security > General for downloads is set by default for "AppStore" and "Apple signed developers" only.
The intention of Gatekeeper is to prevent less savvy users from installing untrusted software, it has a side benefit of causing users to erroneously think AppStore is the only place to install software on their machine, thus Apple benefits by making a commission on each sale of AppStore software.
AppStore software has particular limitations placed on the developers on what they can do with their software. Some developers have a AppStore "hobbled" version as well as a fully featured version if downloaded from their own website. AppStore software also is severely delayed in getting security and stability updates as Apple takes it upon itself to review each and every version. So for faster updates, it's likely best to use the developers version from their website.
If you trust the source or location where your downloading and installing software from other than Apple signed developers or AppStore, then your free to bypass Gatekeepers strict restrictions by holding the Control key down or Right Clicking on the Program, App or Installer to run it. Once it's known as a "trusted app" it will not bother you again about running it, provided it doesn't show up as know malicious program.
Warning! Contrary to the popular belief saying "If you don't give it your Admin password it can't do anything" is not entirely true. Simply running a malicious program in any user account can cause damage, it just can't as quickly gain root access to do the most damage right away, it certainly can encrypt your files or delete them, or install a keystroke logger and communicate that over the Internet, alter other applications and install a bigger payload of itself later.
The Dock doesn't contain real programs, those are what's called "Aliases" or Windows users would know as "Shortcuts" which direct to the actual program, file or folders located elsewhere. To show the location of the real item in the Dock, right click and select Open > Show in Finder. The item there is the real thing, that's what is dragged to the Trash to delete (then Finder > Empty Trash to permanently delete it).
To delete the icon off the Dock, merely drag it's icon off onto the Desktop area and release, it does a puffy smoke thing and disappears.
If you see a question mark icon in the Dock, that means there is a Alias that doesn't know where the original file is located, likely the original file was moved or deleted. Thus when clicked changes to a question mark like it's asking "Where is it?". To remove the question mark, simply drag it off the Dock onto the Desktop and release.
To place a mistakenly deleted Alias off the Dock back on or to place a new Alias on the Dock, locate it by clicking on the Smiley Face in the Dock to open a new Finder window, then navigate to it's actual location and drag it's original item into the Dock until it makes room and release. If you accidentally drop the icon on the Desktop, place it back in it's original location first, then attempt the Dock again.
Some items dragged to the Dock like folders and files will only fit on the Dock down near the Trash Can area, be careful not to place the original item into the Trash and then Finder > Empty Trash as it will then be gone!
Rather double click on the Trash Can to open it and drag the misplaced items back to their original location before trying the Dock Alias attempt again.