(With apologies to TRT):
Step 1:
Highlight what it is that you want to copy. (If it's a web link, to post in an AB thread, the best way to do that is simply to right-click on it. If it's just a block of text, drag your cursor over it).
Step 2:
Right-click (unless you've already done that anyway, as above). Select 'Copy'.
Step 3:
Go to where you want to paste your link/text. Right-click and select 'Paste'. (If you're posting a link in an AB thread, don't expect it to go red on your screen straight away. That only happens after you've clicked 'Submit' and AB's server has turned it into a clickable link).