First, log into MC. Then, select Multiplayer, then select either Direct Connect or Add Server and put in the server ip (play.wynncraft.com or play.wynncraft.net). Now, if using Direct Connect, press the button to connect. If using Add Server, press the button to add the server, then double-click it from the server menu, or press "Join Server" with it selected.
After opening the menu, click any of the options that appear to join any of these servers. Upon joining, select a class by clicking the one you want.
Now use W, A, S, or D to move, left click to attack as a Warrior or Mage, and right click to attack as an Archer. Move around your mouse to look around.
Any additional controls can be found by pressing Esc, then selecting "Options...", then selecting "Controls...".