This is an easy one. First, you must have access to the toolbar, so either quote, edit, start a thread, or hit .
Once you have the access, simply highlight whatever text you want to embed the link into, and then click on the "Insert/edit link" button, represented by two chain links linked together.
A small window will pop up. Simply paste whatever site you want to link to, click "Update", and you're done.
If you want to remove such a link, you must also have access to the toolbar. Once again, highlight whatever text you want to remove the embedded link from, and then press the "Unlink" button on the toolbar, represented by a broken chain link. That's it.