First, movement. To move around with the keyboard, either use the arrow keys, or the numeric keypad. The latter is preferable  With the mouse, left click where you want your character to walk to. That's all! To run, hold down the shift key while moving. Running takes energy, so it can only be done for limited periods of time.

Attacking is similarly easy. With the keyboard, walk up to a monster and point in their direction. Then press the Ctrl key to attack once, or hold it down to keep attacking. With the mouse, left click a monster or player to attack once, or hold the left mouse button down to keep attacking (note: clicking on friendly NPCs will not attack them - instead, it will initiate a conversation).

It's handy to know how to pick stuff up. The method is very similar to attacking. With the keyboard, walk on top of an object and press Enter. With the mouse, left click on the object, and your character will walk over and pick it up.