It really depends on the FC and how they want to introduce people. Some RP FCs will require an IC review or interview, and you'll be invited based on those principles. Some FCs will want you to fit in as a person and will work to incorporate your character afterwards. It's best to contact somebody in the group to figure out exactly how their recruiting process goes, and tell them your own preferences for how you want to handle things.
Leaving is completely different, and will depend on whether you depart with the FC on good terms or bad, how quickly or slowly it happens. If you don't find the FC fun, or don't find your character fits in IC, then try and leave on good terms. If you wish to roleplay a scene out where the character leaves, let somebody know. Both leaving and joining are based on clear channels of communication, though it's not always so simple.
Leaving is completely different, and will depend on whether you depart with the FC on good terms or bad, how quickly or slowly it happens. If you don't find the FC fun, or don't find your character fits in IC, then try and leave on good terms. If you wish to roleplay a scene out where the character leaves, let somebody know. Both leaving and joining are based on clear channels of communication, though it's not always so simple.