To start click on the difficaulty you want. The goal of the game is to find all the fields without bombs. Click on a field to find out what hides beneath the field. The numbers signal how many mines are on the adjacent fields. If you think it is a bomb you can mark it with a flag or questionmark by rightclicking.
If you want to resume the game click on the button above. One the other hand, if you are having second thoughts about wasting your time on this, you are probably right! What does it all matter in the end?