hi i just complete the Adult and Master Class Quest Guide , but i dont know how to use the weapon , plus what else is there to do , and how do you enter the tournaments , plus sorry if these are stupid questions

Their are certain moves that activate the weapons use, until then im pretty sure you don't use the weapon just for regular fighting.

When Korin gives you the weapon right click it, it should give you a new quest on a differend land.When you reach your quest npc it will give you the actual weapon and teleport you to a NPC of your class.After you beat it you'll gain your class title and you'll be able to use your sub-weapon.

ive got the subweapon , im askin how you use the weapon

You only use weapons when using skills that require them. You cannot attack normally with your weapon.

how do you kill that huge sabaimen thingy

you attack it lol jk im not an adult yet so idk

if thats the turtle hermit master class all i say is attack run