How to attack monster / player?
Many mobs attack themselves, when the player will come too close. Whether the mob attacks depend on the level we have, and on how much health we have at the moment. Naturally there are some mobs, which don't attack anyone, and in some places mobs are aggressive no matter how strong and healthy the player is.
If we want to attack monsers, or other player (other players can be attacked only, if they stand on the red / violet field, they have red skull, or they are in guild, with which we have war) we have to click on him LMB, and choose fight icon and our character will go to him and attack.