Plenty of info on the net.  I presume you mean pickling freshly picked ones. ?
Make sure the fruit is clean and free from fly bites (it's a bit early to be picking them yet).  Chuck them in buckets and cover with water with a plate on top to hold them under the water.  Change the water every 24 hours for 10 - 14 days.  This takes away the bitterness.  Boil up enough water for pickling and add salt until no more will dissolve (or until an egg floats in it).  Cool and pour over the olives in air tight jars.  Add herbs/slice of lemon/garlic for flavour if desired.  Top up the jar with half an inch or so of olive oil to keep air off fruit.  Store for 6 months before eating.