Car acts like it will start won't crank over on 2004 Chevrolet Cavalier

The car battery is good, it starts like it wants to crank, but doesn't turn over...need to get information on what the idle throttle control (some one suggested it might need a cleaning because it was clogged??)does, or maybe a Engine control module...could you send me information on what these 2 parts do, and if they are easy to fix...

Cranking = the act of attempting to start the engine!
Starting = the act of the engine running!
Wont crank or wont start?
won't cranks like the starter is good, it is just not starting.......sorry.
First the ignition needs to be checked for spark! If spark present then the fuel system needs to be checked!
So check for spark and fuel pressure. If not equiped to do so, mechanic needed to check it out hands on!
Thank you.
You bet!