Green olives as the name suggests are picked from the tree before they ripen. Black olives are then the ripe ones, to be more precise, those ripened on the tree. There are about 14 varieties classified in Spain: Blanqueta, Callosina, Arbequina, Gordal sevillana, Cornicabra, Manzanilla cacereña, Villalonga, Serrana de Espadán, Morrut, Changlot Real, Canetera, Alfafara, Hojiblanca, Carrasqueño de Córdoba with a whole lot of local synonyms. No need to say that other countries in the Mediterranean like Italy, Greek, Syria, Turkey have their own.
Before serving the olives, some preparation is required to get rid of their normal bitterness. You may buy them canned or bottled but there's the possibility of dressing them on your own. Green olives like the ones you see in the image, acquire that final salty spicy flavor from the extra ingredients people put into the dressing. Don't bother taking those in the bottle to make your own home-made concoction. You need them clean to start with, without previous treatment although it says they are salt free. Once you manage to buy them free of salt, you put them in water to get rid of the bitter taste, change the liquid every 12 hours till the greenest of them tastes sweet. If you don't cut them into halves or squeeze them first the process will take longer. The more you squeeze the shorter the time. The container where you place the olives must not be made of metal nor should you use any metal object or your hands to remove. Once sweet, they are ready to take that dressing. The dressing is applied by layers and shall cover the content. They will acquire maximum flavor in about a week. The ingredients depend on you although there is a certain limitation of course. You may use garlic, thyme, laurel, oregano, paprika, cumin, fennel, orange shells. Remember the basis is water but you can add lemon and/or vinegar. I am not a cook myself and cannot take responsibilities for the right results here but in essence, you may come up with some tasty aceitunas aliñadas in the end.