Hi I just purchased a 77 E 27 and I dont know how to rig it I found sails and the mast is already stepped and the boom is attached but I don't know how to rig tthe boom it is hooked to the rear stays in the storage position.
Congratulations and welcome to the club. As far as the boom, there are slight variations, but on my 27, there is a short wire rope that is attached to the rear stay that I use only for long-term storage. Otherwise, I have a Topping lift that goes from the mast-head, and attaches vial a shackle to the end of my boom. This stops the boom from hitting the deck when the main sail is stowed.
Is your main sheet rigged or not? When storing the main on the boom, I sheet home the main sheet, and that's what keeps the boom from moving side to side. Others may use a boom vang.