All of your basic actions in Demon's Souls are laid out for you in the tutorial. They are also clearly labeled in your manual :) So either way you can get to them quite easily.

Your attacks with your right hand are with your R1 button. Your shield is usually in your left hand, so you use the L1 button for that.

R2 - strong attack

L2 to parry, then R1 to riposte

Note that this combination requires very fine timing, some feel it's not worth it to try. You can easily expose yourself to more damage :)

X - read pink messages

Triangle - dual wield

red line - health, you need to eat things to recover it.
blue line - magic and faith, this doesn't auto regenerate, you have to eat things to recuperate it
green line - stamina, used when you swing swords and such, this auto regenerates

Demons Souls Walkthrough

Demon's Souls Review