Boot disk

What do you mean by a "boot disk?"

Not knowing what you tried:

Download the El Capitan installer from the Mac App Store. After download it is in the Applicatins folder.

THen download and install this app

http://liondiskmaker.com/

and make bootable USB media

I have found this to be very easy, Create a bootable installer for OS X - Apple Support

Are you trying to make a bootable USB flash drive? If so, then do this:

You will need an 8GB or larger USB flash drive that has been partitioned and formatted for use with OS X.

Drive Partition and Format

1. Open Disk Utility in the Utilities folder.
2. After Disk Utility loads select the drive (out-dented entry with the mfgr.'s ID and size) from the side list.
3. Click on theErase tab in the Disk Utility toolbar. Name the drive, "MyVolume".
4. In the drop down panel set the partition scheme to GUID. Set the Format type to Mac OS Extended (Journaled.)
5. Click on the Apply button and wait for the Done button to activate. When it does click on it.
6. Quit Disk Utility.

Open the Terminal in the Utilities folder. Paste the entire command line below at the Terminal's prompt:

sudo /Applications/Install\ OS\ X\ El\ Capitan.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ OS\ X\ El\ Capitan.app

Press RETURN. You will be asked for your admin password. It will not echo to the Terminal window. Then press RETURN again.

Wait until you see the return of the Terminal prompt signifying the process has completed.

tavitar wrote:

TThat's the problem... It says it's already installed. I click download, and it does nothing.

If you cannot download the installer, all of the instructions in all the land will not help.

After clicking on Download, do you get any error messages?

Where are you clicking the Download button?

Look in your Applications folder for Install OS X El Capitan. I'm not sure you are going to find it though as the response to the command Kappy posted indicates the file isn't there.

There is no need to make a bootable installer disk as you can just boot into Internet Recovery and install on the blank SSD after using Disk Utility to format it as OS X Extended (Journaled).

It will take a little while and it will also install the OS that shipped in your Mac. You can then Upgrade from there.

Obviously, it would be a shorter process with he USB installer, but that seems to be problematic too.

If you have the current install backed up with Time Machine, Boot into Internet Recovery (IR) and Restore from your Time Machine backup. You will first have to format the blank SSD using Disk Utility in IR.

You don't have the downloaded installer in your Applications folder or if you do you have renamed it. Have you downloaded the installer from the App Store?

See:

About OS X Recovery - Apple Support

Start up from OS X Recovery

To start up from OS X Recovery, hold down Command (⌘)-R immediately after turning on or restarting your Mac. Release when you see the Apple logo. If you can't start up from OS X Recovery, try holding down Option-Command-R to start up from OS X Internet Recovery*.

You may have to try Internet partition since yo do not have a Recovery partition on your new disk.