New seller Amazon uk question

Evening all.. ok so very new to amazon seller going the FBA way.. if for example i sell something dont know ’12 cans of deodorant’ do i have to have all 12 in 1 box or can i send them loose for them to pick 12 to send to the customer? bsically if im selling several items in a unit do they count and package or do i have to box 12 ready? thanks