If you're a seasoned seamstress or a hobby sewer, you'd have probably learnt this first thing as a kid. But there are quite a lot of people that have no clue how to sew on a button. Its easy!
I've included a needle threader if you're not very good at threading a needle.
Make sure the eye of the needle is large enough to fir through the thread doubled over.
Push the wire loop through the eye, then push the doubled thread through the wire loop. Pull the threaded away from the needle. Match up your thread ends and knot. Should be 4 lengths of thread.
Push the needle through from the back and fold along the mark where the needle came out. It doesn't matter which way you fold it. Horizontal or vertical, but if your stitching on a row of buttons, like on a shirt, you'll want to fold the same way for each button so the stitching is consistent.
The right side looks obvious on my sample button, but its not always, so decide which side is the right side.
Hold the button to your folded garment, with only half the holes pocking up over the fold, so I have 2 holes showing, my button is a 4 hole button. You should be looking at the underside of your button.
Thread the needle through one of the holes and pull through.
Turn the fold over slightly so that you can see the right side of the button and push the needle though the holes that are not visible from the starting side. You should be sewing though the fabric.
The needle will be back in the starting position. Do this step for the other side.
This is what it should look like. Because you've double your thread, you don't need to stitch too many times to make it strong.
Nest step is to loop the thread around the stitching between the button and garment a few times, then push the needle though to the back.
Push the needle through the back a few millimetres to create a loop.
Thread the needle through the loop and pull tight. You can repeat this to make sure it doesn't come undone.