One way to connect two pieces of leather together is to use rivets.
It is very simple. Hold the two pieces of leather together, punch or drill a hole in both. Put base part of the rivet through both pieces, then place the cap on the rivet base. A small tap of the hammer and the rivet is set.
The setter is a tool that comes with the rivets. It keeps the domed cap the proper shape. A lot of rivets can just be set with a hammer if you have no setter.
There are lots of different sizes. You just need a rivet base that is the approximate thickness of the two pieces.
For two pieces of leather, I use mini or extra small.
This is what it looks like when they are installed.
Even with no sewing or any other means of attachment, the rivet can keep the leather in place. And it looks great on armor pieces.
Rivets are very strong, and easy to install. There is no sewing needed with them, and they come in different colors and sizes.
Go ahead, make a mess, rivet something together, have some fun.