This is a term that covers a lot of ground. Some are more a talk on "How I Write Songs," with a few tit-bits of information on how that person goes about his/her craft, accompanied by a few of their songs to illustrate what they do.

Others are a more of an encouragement to actually write songs, by perhaps giving a theme, or song title and getting everybody to jot down their thoughts, or as in one case, one person wrote a first verse and going round the folks there, they all wrote a verse, or contributed to a verse, until a song was complete.

So, generally speaking, it can be a talk, or a practical song writing exercise. No doubt other will know different approaches, but these are the ones I've seen so far.