Well this is pretty simple
If you are part of a team and wish to apply for a mission just post a topic here, put the team name/number as the subject and whatever else you feel like post on it. The in the topic roleplay as if you were asking the Kage of your chosen village for missions. If there are no characters that are RPing as the Kage of your village then a chosen Admin will temporarily act as said Kage and give you a mission. This is to keep the site going and you can roleplay properly as a team.
If you have specific ideas as to what kind of mission you wish to do just leave a bit of info in the post about it and the person acting as the Kage shall give you a mission as you requested. Also
..you may just wish so discuss with someone here whether you may have a mission or not. In that case feel free to just post asking for a mission then an Admin can provide you with a temporary team, as they would in Naruto, and give you a mission to do. By posting other members can then post in the topic asking to join on the mission and an Admin can help you to sort it out.
If there's anything i've missed please feel free to ask Have Fun <3