@Mega
You know how you have to make an id for your mii when you first made your mii? That is the id you use to add friends. The easiest way is by Miiverse.
AS for Monster Hunter, You play as a hunter and go on quests and hunt monster, mainly wyverns and dragon class monster but there are others. I've been hunting for many years now. Oh and the game is skill based. You need skill to play, no leveling involved, except for rank.
For more info, use this site, it's what I use.
http://monsterhunter.wikia.com/wiki/Monster_Hunter_Wiki"No matter how strong or what power the enemy has, I will fight and protect my friends, even if it cost me my life to protect them. I will fight until I die to ensure their future."