The aft-most block and the clam cleat ahead of it are for your outhaul.. it should run from the padeye opposite, through the clew cringle on the sail, back and through the block to the cleat. I expect the padeye on top of the boom aft is for a topping lift.
The other two blocks (each with a padeye opposite) would be for the mainsail clew reefing lines. The block and cleat near the gooseneck may be a tack reef or more likely a cunningham adjustment.
What boat is this on?
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)