If you are new user with post count less than 10 you are not allowed to post the links. This is done mainly to stop people from spamming just after registering and as soon as you get into double digit post count this restriction goes away.

If you still want to post link try skipping the http and www part in the link and you would be able to make the post but the link would not be clickable.

If you want to make the link clickable you can let me know and I am more than happy to do it for users.