Olives are disgusting straight off the tree. Commercially they are cured using lye, eg. caustic soda, which neutralizes the bitter taste. After which they are pasteurized. I prefer to do it with water and keep them raw.
After picking the olives make a cut in each one. Don’t wait till they are dark and soft
they are for the Sun Olives  recipe. Wash them and put them in water. Now change the water twice a day. After a week or so I start tasting the olives, as soon as they taste good it is time to prevent them from going off. For example by putting them in a brine (salty water) or in olive oil with some herbs, like oregano or thyme.