If you have a good understanding of computing distance of a point to a plane, then you can understand the SAT without too much trouble. So be sure you understand this kind of code:

d = Dot( plane.normal, point ) - plane.offset;

or

d = Dot( plane.normal, point - plane.pointOnPlane );

You should able to answer questions like "what happens when we dot a normalized vector and a vector together", or "should this vector be normalized" (sign testing), while working on this kind of collision detection stuff.

Once you understand these you can try reading something like these:

http://www.randygaul.net/2013/07/16/separating-axis-test-and-support-points-in-2d/

People also seem to really like that "N-Tutorial", so you might like it too.