PCA in their wisdom decided to make it a little more complicated when posting links and did not think it necessary to sticky the instructions at the top of the forums. You are certainly not the first to ask the question how to post a link correctly and will not be the last.
If you click on the blue globe top left of the message box a box will appear where you can enter your link, this usually means making sure that the HTTP:// that is already there is cleared. then click OK,you will see Enter link description here highlighted in blue, put what you want there. Job done.