Excel 2007 : Updating results across sheets automatically?

Hi guys i am a new user to excel and forgive me if this is too easy.

From the attached sheet ( its a bit of a mess), i am trying out a football ratings system.
Basically i am trying to auto update the home and away power ratings after each game from entering the results each week.
After the results are entered in the second game (A16 to E21),
the HOME ADJ (Column L) and AWAY ADJ (Column N) are updated.
I would then like to add these to the POWER RATINGS on Sheet2 and have the value automatically updated.
The same for the next match and so on...

Clear as mud!! LOL

I dont know if i am approaching this correctly from the start but, hey you gotta start somewhere!

Many thanks for your time it is much appreciated.