Foty,
Best thing to do is set up a test rig then do a few simple exercises.
I would suggest wiring up a power supply, CPU, 1 input and 1 output card.
Next connect it to the PC.
Next program a simple latching on/off motor starter circuit in OB1.
Next transfer this to FC 1 and call it from OB 1.
Next modify this to use FC1's I/O variables, and call this from OB1 three times for three different sets of I/O.
Have the siemens help line available, and read the manuals carefully.
The above steps seem simple, but there are a few catches to them. It will probably take you several days to complete them.
Once you have finished this, you can start to play around with timers and other cool stuff.
Doug