The end where you apply your force is called the Effort arm, labeled "e".  The end where the rock sits is called the resistance arm, labeled "r".  The rock can also be called the Load, labeled "L".
 

If the rock has a mass of 100Kg and the effort arm is 2m and the resistance arm is 1m, how much lighter does the rock feel?
To find our answer, we need to know how to find the MECHANICAL ADVANTAGE of our lever.
For a lever, MA=effort arm/resistance arm, so our answer is 2/1=2.
The lever makes the work of lifting the rock twice as easy... in other words, it feels like only 50Kg.

What if we move the fulcrum half a meter closer to the rock?
Then our effort arm becomes 2.5m and the resistance arm is shortened to .5m...
so our MA= 2.5/.5=5.
Now the rock feels 5 times easier to lift, same as only 20Kg!