I like to pickle about 5 kg now but the first time I did it I had 3 kg and this is plenty to get started. Don't go for the big ones - I think small ones have a much better flavour and pack better in the jars.
3 kg black olives (I have never done it with green ones)
3 Tbl salt
12 Tbl olie oil
600mls white / cider vinegar
1.25 litres water ( boiled and cooled)
optional : 1 clove garlic / jar
1 small red chilli (or less)/ jar
dried oregano or other herbs
After picking , wash then slit each olive on 2 sides. Place in a large bowl and cover with ordinary tap water.
Change the water daily for 10 - 14 days, until you can bite into one and not spit it out in disgust ! It should still have flavour but not be unbearably bitter.
Sterilise some jars (I find 3kg makes about 12 medium jars) . Place olives into jars . Putting in some / all / none of the optional ingedients as you go.(I usually don't use any now because I prefer the real olive flavour)
Mix the boiled water, vinegar, salt and olive oil in a bowl. Pour into the jars making sure you cover the olives completely. Put on well - fitting lids.
That's it. Wait at least 2 weeks before starting to eat. You will find the flavour changes with time - some people prefer them with the ' fresh' taste you get after 2 weeks, others prefer the more mellow flavour after 6 months or more.
They should be stored in a cupboard but when you open a jar put it in the fridge if its a big jar / you think you might take ages to finish the jar / if the weather is hot. I always put open jars in the fridge in summer or they go mouldy, but I never do in winter as we eat them pretty fast and I don't use huge jars.
Good luck. Give me a ring if you have any questions or if you have any spare olives you don't have time to pickle !