I've never thought much about the classes of lever. I have just got on with using the Principle of Moments to solve them. However, there's a lot of stuff out there about the types. The difference seems to be about the order in which you find the three elements. In the case of class 3, the effort and the pivot are both on one side of the pivot but the effort is nearer to the pivot. By the Principle of Moments, big effort force x small distance = small load force x big distance. It's a distance multiplier.
