Olives are pretty much inedible when fresh, so you have to pickle them in brine. There's lots of recipes on the net, and they all vary quite a lot. That's a good thing; it usually means that the details don't really matter too much.
Fresh olives are very bitter, so first you need to soak them to remove that flavour. We cut the olives in top and bottom and put them in a jar. We poured a brine of 1 part salt to 8 parts water (by weight) in the jar, then used a small glass lid as a weight to keep the olives below the surface.
Our olives just after the second pickling.
It's been two weeks now, and the olives have turned a muted olive green and the brine has turned brown. We strained the olives and washed them in fresh water. The bitterness is gone and there's a faint but definite olive flavour. But they're still kind of raw and crunchy, so we put them back in a clean jar, mixed another batch of brine and added two halved cloves of garlic and one sliced dried chili. Top up with olive oil as a "lid" to avoid contact with air, then put the jar back in the closet again.
The major worry is that they will spoil. If they don't, they should be edible in about two months or so, just in time for the year-end holidays. I'm looking forward to trying them.