If you want to advertise your forum, just put it in your sig.
How do you make a link? Look here and copy and paste this code in the signature box:
[a href=
http://www.website.com]Text[/a]
replace the www.website.com part with the link of your forum and for the 'Text' part, put whatever you want like "Visit my forum!" or whatever you want. Then get rid of the [ ] parts and replace it with < >
Where is the signature box? Go to Settings and scroll down to see the signature box. Then just click save settings and you will see a confirmation screen.