AppleScript: Please explain these two commands

[J Christopher]

I was reading this post, and found the following AppleScript:

-- Hit the Tab-key
delay 1.0
set timeoutSeconds to 2.0
set uiScript to "keystroke tab"
my doWithTimeout(uiScript, timeoutSeconds)

Could someone please explain:

set timeoutSeconds to 2.0

and

my doWithTimeout(uiScript, timeoutSeconds)

What, exactly, do these commands do?

Thanks.