'91 Chevy S-10 pick up 2.5 4cyl wont start

Ok, when trouble shooting a non starting engine, you test for three things. Fuel, Spark, and Timing.
So, are you getting fuel to flow? You can usually smell it if it doent start and fuel has been flowing thru your injectors.
Are you getting spark? You can lay a spark plug on top of the engine connected to the spark plug wire and see if it fires as you turn.
Last you need to see if the spark is sparking at the right time. You will need a test light for this, or maybe ask a friend to check it for you.
Usually if you are off just a little, it will fire some but not stay running, or run very ruff. If this eninge is not firing a bit, then it probably is ignition or fuel.
Have you checked your engine compression? If your timing chain has broken, you will probably have several cylinders iwth good pressure and one or more without pressure.