campaing logs are basically tales of the story. they can have many forms: from the players point of view, from the character's, from the DM's (like mine is) or just a general narrating of the story.

different people writ in different styles- some serious, some humerous, some adding stuff from the players, some strictly to the story, and so on.

all those i've seen that dealt with actual modules (most don't) write it clear at the opening post.

it's really up to you which ones you like. the most famous collection is the SilverClawShift Campaign archives which many people enjoyed immensely- really good!

they are a good source of ideas, and how others do stuff, in an entertaining way. they can also be interactive, with the author answering questions by readers or (such as in my case) sometime asking advice.