Here's your tutorial, Fitty:
Step 1 - Right-click on the Web Address on the Address Bar of your Browser (Chrome shown here, but the process will be similar for all browsers) and choose "Select All":
Step 2 - Right-click on the Web Address again and choose "Copy":
Step 3 - Click on the link button at the top of your messagebox in the formatting options (it looks like a chain link):
Step 4 - A separate pop-up will appear that looks like this:
Step 5 - Right-click in the empty box next to URL: and choose "Paste":
Step 6 - Now that your link is in the box, just hit the "Insert" button:
Step 7 - You're done! The address is in your message and it is now a clickable link:
NOTE - If you want to link an image or media (YouTube) instead, the process is exactly the same except instead of the chain-link icon, you'd press the image button or the media button.