To mine you need to head over to here: https://nulledbb.com/credits/?action=mining If you're going to mine, it's going to take a while to get anything worthwhile. The amount of tokens you collect x the exchange rate will equal how many credits you mine. It's going to take a really long time if you don't have a good CPU. it's much faster to just engage with the community and earn points that way, though mining does help the forums I guess...
"It never hurts to keep looking for sunshine" - A. A. Milne