Ok, here goes!
First, I took the same photo from the website you bought your snaps from and labeled the pieces A, B, C, and D. See here:
now, you will need a setter tool, first of all, do you have that? The bottom piece of the setter tool is circular, and has two sides. one side has a smooth surface, and one side has a small raised dot in the middle. Just take note of that for now.
Ok, onto the process..
1. Take your fabric and make a small hole where you would like the snap to be. Then position the other piece of fabric for the other half of the snap, and make the second hole. So, in essence, you have two pieces of fabric that you would like snapped together, and where you would like the snap to be, you've just put two holes instead.
2. I like to do the bottom snap first, so this explanation does it bottom first. Take the piece of fabric that is the bottom "under" piece. Get out your round setter tool, and put the circular part of the tool with the raised bump side up.
Now, take the snap piece "C" and put it on top of the snap holder:
3.Now you put the holder with the snap piece "c" under the BOTTOM of the fabric piece that you already put a hole in, so that the post sticks up and out of the hole in the fabric. (fabric should be right side up) Now you put snap piece "D" on top of that post, so that your fabric is sandwiched in between the two snap pieces. Now take your long setter, and put the tip of it over the post that is now sticking out through piece "D". Hammer 4 times or so, not too hard or else you'll just make a squashed mess:
4. Now it's the same process for the top snap. To start this, take your circular snap holder, and turn it over so that the smooth side is facing you. Put your snap piece "A" in there. now put your fabric, right side DOWN over the post of A, and then put snap piece "B" on top of the post sticking up from "A", and put the setter tool tip on top of the post, and hammer:
Now you should have both top and bottom snap pieces set:
and snapped together:
so,, does any of this make sense?