Whats the difference between substitution and elimination

In substitution you attempt to isolate one variable, plug it in, solve for it, plug it in again, then find the second variable. Sounds complicated but it isn't.

In elimination you add and subtract.

Example:
x-2y=4
and 
x+y=10

For substitution:
Isolate the x on the top equation to get
x=2y+4
Plug it into the 2nd equation.
2y+4+y=10
3y=6
y=2
Plug it in to solve for x.
x+2=10
x=8

Xis equal to three