Must be an FAQ on this somewhere:

Go to the page to want to share, and copy its address, - right click on the URL in the navigation box and select copy".

Then come here

Click on   Make a link ("blue clicky") below right.

Paste your URL into the top box (ctrl-V).
Enter any text you'd like (e.g. Watch be play underwater!) in the lower box.
Click
Create Link.
Copy the link created... that's everything from < to > inclusive.
Come back here and paste it in.

Job done!