Have the URL in the clipboard. Click the "view more" button when you are entering your post and drag-through a word or words you want to have become the link to 'select' them. Click the chain link icon above your typing and a new box will appear, here you paste the URL from the clipboard in the lower entry box and click 'Submit query. That's it. You can go back and color or modify the text that you just made into a link, but be careful, modify only the words, not the whole string.