A few questions about AppleScript (that I’m annoyed about)

> Why is my AppleScript not working

In your first script you use choose from list.

choose from list always returns a list as its result. Even if there's only one item selected, it's still a list.

Therefore, if the user selects, say, Safari, the result is:

{"Safari"}

i.e., a list containing a single string.

This is not a valid parameter to the tell application command. tell application requires a string, not a list.

The simple solution is to extract the string from the list, via something like:

set theApp to (choose from list {"Safari", "Chrome", "Scripts", "App store", "Mail", "Facetime", "Messages", "Notes"} with prompt "Choose an app to open" with title "Some applications to open")
set theAppName to item 1 of theApp
tell application theAppName
	-- code goes here
end tell

Note how I use a new variable theAppName to extract the first (and only) item from the list.

> The second question: What does "ignoring" mean in AppleScript?

AppleScript has a number of rules it follows when running. ignoring... overrides those. It has a corollary of considering.

For example, text comparison is normally case-insensitive, but you can control this via the ignoring|considering case statement:

ignoring case
	"a" = "A" --> true
end ignoring

considering case
	"a" = "A" -- false
end considering

Other things you can ignore/consider include:

application responses - normally when AppleScript sends a command to an application, it waits for the result. If you don't care about this (i.e. you want the command to execute in the background while your script moves onto other steps), you can use ignoring application responses.

punctuation - Normally the string "Hello, world." and "hello world" would not match, but ignoring punctuation ignores the commas, periods, etc. so they do match

There are others, too.

> Assuming the user clicks "Cancel," it will display the error "Error: -128. User canceled." It seems it is just making variables out of nowhere according to how it compiles

For this, you have to understand what try/end try does.

When any command fails it returns two variables, the error message and the error number. These can be used by the developer to determine what action to take (ignore, bail, alert the user, etc.).

Normally when this happens, AppleScript itself posts the error message in a dialog. However, when using a try/end try statement, these variables are exposed to your script so you can take whatever action you like. In this case, the line:

> on error the error_message number the error_number

catches the error and puts the error message into the variable error_message, and puts the error number into the variable error_number.

In the case of display dialog, clicking the 'Cancel' button automatically triggers an error -128 with the message 'User Cancelled', and that's what's passed into the on error handler.

Additional to Camelot's responses, you may find the Apple AppleScript Language Guide useful in choosing correct syntax.