There is nothing special about getting involved... you don't even have to wear a costume. Getting involved could mean just talking about it. Maybe you just want to help out designing or making a costume.
The typical places to wear cosplay are things like conventions, movie premieres, or related events like the release of a comic at a comic book store or a movie blu-ray at a store where they have a big display.
There is not good answer without knowing the type of costume.