Okay, Clan Wars are held about every other week starting on Wednesday and ending Monday, you do not initiate anything. If you have a clan and it is placed (Bronze through Gold divisions) then when a War begins your clan will automatically be placed on a leaderboard with 7 other similarly ranked and membered clans and during those five days you will have the opportunity to fight for nodes to acuire points.
If, however, your clan is not placed in a division (I don't think 3 members will place any clan even in Bronze, I might be mistaken but you need 5 at minimum) then it will not be able to compete in a War until it becomes ranked. This Wednesday the next war should start, if not then the following Wednesday, keep an eye on the app home news ticker for announcements.
In the app there is also a Clan Wars FAQ which will tell you all of this and more.
As long as you have at least 3 clan members you are automatically enrolled in clan wars.,,, the next clan war looks to start 6-18-2014 they have stated on treybeachhead twitter that they will not have clan wars over Father's Day ,,, there is no official schedule for clan wars but it typically has been every other week ... To keep up to date you can keep an eye on the news feed on the app , follow beachhead twitter ,, treybeachhead twitter , and you can also check these forums GHOSTS CLANS DISCUSSIONS because usually after information is released someone will post it there.
dont worry about it saying your not registered as long as you have at least 3 members you will automanically be enrolled In bronze through platinum division. Heavy deciding factor for placement is how active your clan is , once your in clan wars there are a few other things that will help determine your placement.