What does this mean? "Players looking for a team"?
Will the team captains actually be able to like pick their own team independent of the guys who are looking for a team?
The captains are obviously able to pick the players they want in their team. When we will chose the first captains (in a few days), they will be able to organize themselves how they want. They can organize selections, post some announcments on different forums etc.
The "players who are looking for a team" are just here to help the captains if these ones are in a lack of members, then they can simply contact the persons who are looking for joining their nation's team 
Just to make sure that I understood what you just said: The players don't need to sign themselves up after all?
Indeed. If the captain himself knows some very good cavalry players, he may call them to the selections. But if a player signs up, he will most likely get called to the selections as well, and then maybe he will get a chance to be in the final roster of the team.
Again, the organization of the team is up to the Captain and his Vice-Captain.
