As you learn better and better abilities, you begin to get into the realm of complex keystrokes to do certain actions. But for 99% of the game, the basic keys will let you do everything you need to do.
These are for the XBox - your manual should give you the matching keys in your own system.
A - quick attack
X - parry / block
Y - strong / fierce attack, can break shields
Left trigger & A - range attacks
Right trigger - killing move (use on a downed opponent)
Black button - action (climb down ladder, fire catapult, etc.)
Basic Level 1 combos:
speed combo aaa
fierce combo yy
The BEST combo that I love is the simple Orc Hewer that you get pretty much right away. It's just AAY. It's very easy to do and works on just about any enemy. I use that far more than any other more complex combo you get later on.
Return of the King Walkthrough