The Guild section originally had just a few main Guilds, such as the Writer's Guild and the Roleplaying Guild. After a while, other members wanted to form other Guilds, such as the Photography, Computer Programmers, Artists etc. A section was made for these Miscellaneous Guilds called simply Misc.
As well as the serious interest guilds which took advantage of this section, other more light hearted guilds also formed. Two of these (the Brooding Club, and the Lazybones guild) have actually proved to be more popular than all the others put together.
As to what you post in this section, it depends really on which guild you have actually opened. Most are fairly self-explainitory, with maybe the exception of the two I mentioned above.
The Lazybones Club, is just a place to hang out and do nothing really. The Brooding Club is a place for you to go and share with others what a rotten day you've had, and support others who've perhaps had a worse day.