The paved floor of the Prairie village is a safe zone. Monsters never chase you onto it, never attack you there and can't land a hit on you while you stand on it. Run back onto the paving whenever a fight goes wrong.
Out in the world, players can't hurt each other. You can hunt next to anyone without worrying about being attacked.
The one place where players fight each other is the Guild Arena. Its entrance is a portal in Bizarre Rock. Inside, every player in the arena can attack every other player. Step in only when you mean it.
Coming later: duels (the Party Duel option in the player menu), clan wars and the war areas (The Bright War Area and The Emperor War Area) aren't open in the alpha yet.
You can already found a clan, invite members (hold Ctrl, click a player, then Relation > Clan), give out ranks and titles, post a clan notice and chat on the Clan chat tab. Clan battles are coming later.