Here is how to make the eye if you want an eye.

Here is how to form the snap.

Snap open/closed

For my own use, I do not make an eye in the top end of the leader. I simply put a tight bend in the end of the wire and tie it to my line with a Bristol Knot.  Here are a couple of leaders, one rigged with a Bristol Knot and the other with a formed loop ready for your line.

I start out with 6" of wire to form a 3" leader.  Leaders can be as long as you'd like, however.

Life is too short to catch little fish.