Hey (again!) waterwoman,
You can either choose to get invited randomly, or you can look through the section of the Forum Recruitments you posted in.
You could also click on the
Global button (3 persons) to the bottom left of your in-game screen, choose
Global Ranking and a pop-up should appear.
On top of the pop-up there should be 3 tabs, 1 which is
Guilds. This will show you all the guilds in your world!
Now if you click on the little castle to the right you will see the Guild's profile, with usually a message what they're about, entrance requirements and guild members.
As for a suggestion on learning the game, there is an awesome
Glossery of Guides.
Enjoy the game!
- L