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These three terms are associated with levers.

Fulcrum = the pivot point of the lever 

Resistance = The load being moved 

Effort = The added force by the lever's user. 

If it's class 1, F, fulcrum is in the middle 

If it's class 2, R, resistance is in the middle 

If it's class 3, E, effort is in the middle 

Examples 

Class 1 lever, see-saw, with a bag of bricks on one end (R), and you pushing down on the other (E), of course, Fulcrum in the middle. 

Class 2 lever, Resistance in the middle. Imagine a board with a hinge on the end, put something on it in the middle, and lift the edge of the board. 

Class 3 lever, Effort in the middle. Engine hoist, or many crane booms that have a hinge point at the bottom and are raised and lowered by a hydraulic ram that connects somewhere in the middle of the boom.