Question
 

You are only allowed to post URLs to other sites after you have made 15 posts or more. -- what is the meaning f this? thank you.

It means you can't post links to websites until you reach 15 posts. It's a way to make sure spammers or robits don't sign up, drop a link and leave. Please note that having 15 posts doesn't give you reign to use MB as an advertising market or bulletin board.

Yes, please note that obtaining 15 posts will allow you to post photos and links, however self promotion and advertisements are still forbidden at this stage.