When you find a web-page or PDF article that you think others might find interesting or enjoy reading you can create a link in the UKB forums to the article for others to click on.
The simple way
The simplest way to create a link is to go the the address bar of the page you want to link to (the bit that starts http), copy this (in most browsers Ctrl + l will move focus to the address bar, then Ctrl + a to select all, then Ctrl + c to copy). Then return to the UKB page where you are creating/writing your post and paste this in at the position you want it to appear (Ctrl + v).
Thats it, when you hit Post the forum will turn this into a hyperlink, albeit a fairly obvious one that is the full address of the web-page that can look a bit ugly.
A slightly more sophisticated way
A slightly cleaner approach is to hide the URL behind some text and make the text itself a hyperlink as is common on all web-pages.
To do this in the UKB forum you need to copy the URL of the page you want to link to as above (Ctrl + l, followed by Ctrl + a, and finally Ctrl + c). In the text of your post you then need to put this URL within some BBCode tags. Start by opening a URL tag...
...then paste (Ctrl + v) in your URL and close the opening tag (the ']' at the end)...
...next type in the text you want to appear as a hyperlink...
[url=http://ukbouldering.com/board/index.php]the UKB Forum front page
...and finally close the URL tag...
[url=http://ukbouldering.com/board/index.php]the UKB Forum front page[/url]
Thats it! When you hit post you will have a link that takes you to the UKB Forum front page
Dealing with PDFs
Sometimes the thing you want to link to isn't a web-page, but a PDF linked from another site. If you click on this link the PDF opens up in your PDF Reader (typical Adobe Acrobat) and you can't copy and paste the URL from your web-browser. You can easily obtain the URL of the PDF by right-clicking on the link to it and selecting "Copy URL" or "Copy Address" (depending on what browser you are using) and paste this as above.