You can move in-game both with mouse-clikcing (the easiest way to me) and keys (W - A - S - D ).

To attack a mob, you double click on it and the character automatically attacks it (only with normal hits). If you already have a skill (you buy it at the correspondent NPC of the starting city), drag it onto the skill bar and it's ready to use. To use it, select a mob (one click only) and right click on the skill to cast it. As the skill alone won't kill the mob, you'll need to use the normal attack (or double-click on the mob again).

On Archlord's main page you'll find an overall guide of many aspects of the game. Read it, it will also help you out with further information. If you can't find what you need, you can always ask.

And yes, Archlord is a pvp-based game. You can start pvping after you're lv 20 anywhere but cities.
When you leave the city, you can be pked or you can pk (it does not mean you step out of the city and someone kills you xD it just mean you're now on a free battlefield where pk/pvp is likely to happen).
There are GvG's too (guild vs guild), Battlground Race vs Race (Humans fight against Orcs, Mooneleves and Dragonscions to protect the Hero of their races; the place itself is a free battlefield and anyone can pk you), Battlesquare (this one is a bit empty, it'll be renewed soon), Guild Battle Arena (for guilds tournaments), Battle Royal (an upcoming pvp area, one vs the rest), Castle Sieges (4-5 guilds fighting each other to win or defend a castle) and every single lvling place in Archlord (some pk for fun, some for spots, some for their allies, etc.-) .

Hope it helps