Pretty sure it has to be 20 posts, and these have to be posted in certain/useful areas of the forum. Not in the general chit chat areas like " The Pub "
Don't just go starting random threads or posting crap to get your post count up either. If you get caught you will cop a ban.
Just to inform you because you are a newbie, there is a search function at the top right of the page. (And a FAQ"S section as well )
You can use this to search for anything in the forum. (You would have definitely found the answer to your question had you used it)
I suggest you use this before posting threads and asking any questions, as some subjects have been done to death over the years, and certain members will not be so polite in the way that they point it out to you.
Anyway, Welcome to the forum