I've been curing olives for quite a few years and have run the range of lye cures, salt box cures and various brines. After a number of variations I find that I'm happiest just using salt and patience. It doesn't get more simple than this but it does take some effort in the beginning and a lot of patience as they cure.
By not using more complicated cures I can wait to decide what to flavor them with and marinate them with herbs, oil and other things like garlic or peppers in small batches to suit whatever mood I'm in at the time. Though most often we simply eat them as they are from the basic brine.
If you don't live near an olive area you can order raw olives online. They range broadly in price.
I arrange ahead with an oil producer who is kind enough to sell me olives from his orchard. I get them for about $2 a pound. In past years even curing 4-6 pounds has left us buying olives by the end of the year. This year I'm putting up about 8 or 10 pounds.
I try to plan ahead as best I can and understand that the olives I put up today will be the ones we are eating the following year. Once you get in the habit it's pretty simple and makes for a nice seasonal family tradition.
Step 1: What you'll need
Salt! Any non-iodized salt will do. I don't know that you couldn't use iodized salt but every person and recipe I have seen or talked to has warned against it. Easy enough to just get non-iodized. I like kosher salt. The important thing is that it dissolves well in water. So, something like a corse sea salt will be fine but take more time. It's up to you.
Jars. Any glass jar you can seal will work. I used wide mouth jars in the past but eventually found I prefer glass milk bottles. The narrower neck makes it easier to keep any floating olives in the brine and we have a steady supply of them as we buy milk in glass bottles. You can use canning jars, apothecary jars or big decanters with bales on them. Whatever works for you. In my case I find a two pound bag of olives fits well in a 64oz/1.87 liter bottle.
A way to heat the water
An uncooked egg
A small sharp knife
A large bowl
Step 2: The brine
You heat some water and start adding salt. I've not bother to measure it in most cases as the ideal according the vast majority of sources is to add salt until an egg floats in the water. That would be an uncooked and unbroken egg.
Gently heat a quart or so of water and add a half cup of salt. You'll need more than that but it's a good place to start. Once the salt dissolves see if the egg floats. If it doesn't, add more salt until it does.
Once the egg floats you're brine is strong enough. Set it aside and let it cool while you crack the olives.
Step 3: Cracking the olives
Cracking the skin allows the brine to penetrate and cure the olives. You can cure without cracking but it takes a very long time with a simple brine cure like this. I have a batch I tried without cracking that's just now edible after almost two years in the brine. That's a very long time for a meal. Though, they are pretty and taste as good as any.
When you score with a knife be very careful not to cut the pits. Fresh olives are bitter as it is and cutting the pit can release even more of the chemical that makes them so.
Once your olives are cracked it's time to brine them.
Step 4: Brine the olives
You want all the olives submerged to prevent spoiling. I turn mine regularly to keep them covered in brine. Maybe once a day at first.
After you add the brine close the container and set them aside. Some will say to leave them in a cool place other refrigerate. I refrigerate mine, no doubt one of the reasons it takes them longer to cure but I feel safer and have yet to trust a cool pantry or cellar.
Many recipes will call for changing the brine several times in the beginning. I have done this and have had better personal luck making a stronger brine and just leaving them be.
I lost a couple batches early on from not making the brine strong enough. Disappointing but I learned from the experience.
If you encounter mold or slime or mushy olives, discard them. Botulism is a real danger in food preservation. I'd much rather lose a pound or two of olives than risk this kind of food poisoning. It can be lethal.
Step 5: So when are they ready?
For me the learning process of repeatedly tasting them as they cured was valuable. Each week they got less and less bitter until I felt like I could eat them. The texture changed as well and became more and more what I had expected in an olive.
If you're olives are too salty you can soak them overnight in fresh water before you intend to eat them. This would also be a good time to marinate them in oil with herbs and other flavorings to taste.
They'll keep for about a week after you take them out of the strong brine.