They are especially good for baby clothing as there is no risk of buttons becoming loose (which could be a choking hazard).
They are really simple to install, but the instructions are pretty much non-existent so I hope the steps below help you out!
Ok, so first thing to understand is which bits are which. For each snap fasten closure you will need 2 covers (the smooth round ones in the picture), 1 male snap (the one with the sticky out bit, they really are called the male!) and 1 female snap (the one with the hollow centre).
First step is to mark where the snaps need to be inserted on each side of the fabric (where the button and button hole pattern markings will be), I simply stick pins in the fabric as shown below.
I then use a darning needle to make the hole a little bit bigger (this just makes it easier to insert the snap).
Next step is to push one of the snap covers through the hole with the spike end facing down (so the plastic cover sits on top of the right side of the fabric).
Next insert the male snap on top of the spike that is sticking out of the wrong side of the fabric, with the sticky out bit facing outwards.
Next use the tool to secure the snap, the snap cover will sit in the white cup side of the tool, and the male snap will be on the clear rubber side, squeeze the tool firmly so that the snap is secured.
Next, use the darning needle to make the hole on the other side of the fabric, then insert the snap cover but this time the plastic cover end will be on the wrong side of the fabric, and the spike end will be sticking out through the right side of the fabric.
Now place the female snap on top on the spike, with the hollow side facing upwards, and repeat the process to secure the snap.
Sometimes they are a little stiff at first so you need to open and close them a few times to loosen them.
If you have any queries just ask below in the comments.