All I ever do is copy and past the link. You can also click on the earth icon in the selections above the box you type in when you post. That will allow you to enter a link.
Just make sure the link is in line with the BOC rules. Here is what the rules say about links. 4. Links to Off-site Data
Links to Personal or Business Web-Pages is authorized as long as it is done for member support. Links must not point to forums, as they directly compete with the BOC. Email addresses should not be posted on the Forums, the Private Message (PM) function must be used for member to member communications. If a link is removed, open a trouble ticket for an explanation.
Links in public profiles:
Members with web sites may place link to their non-commercial home page in their public profile, WITH BOC STAFF APPROVAL, by reciprical link arrangement, where member places a prominent Reciprical Link to the BOC on their home page.
If you wish to take advantage of this option, contact BOC Staff for Approval, provide member name and url to your homepage in the trouble ticket.
Staff can provide you a copy and paste HTML code for your home page
All depends on what type of link and where you are trying to add it.
I hope this helps.