you should be able to post links just fine simply by writing the link in the post.
There is also a little button in your reply, or quick reply, box that has a little chain link that lets your insert a link. You can click on that. and write in the link in the part that says URL. if you are having an issue with it, please let me know as it might just simply be a site setting that's activated that prevents new members from posting an external link if they are brand new. (usually with that setting active that would mean you need to wait at least a week of joining in order to be allowed to post external links.)