how do i fill in v5c logbook?

i am selling my car to a local garage do i fill in section 4 of the log book which says selling transferring or part exchanging this vehicle to a motor trader if so does the vat number have to be given or it doesnt also the other thing is when i give the logbook which part do i send off to the dvla and which part does he keep like does he have to keep the main log book with my name and address on it and i just take the yellow slip and tear it off and send it to dvla im new to this dont know much about the logbook just dont want anything dodgey to happen if log book is on my name. if you guys know about this let me know thanks.