Ship's boys were the youngest members of a ship's crew. They acted as servants to the warrant officers or officers as well as performing other tasks aboard ship. For example when raising anchor, they acted as runners, each in charge of a 'nipper', a cord used to attach the anchor cable to the messenger cable which went around the capstan drum. In battle, they were powder monkeys, fetching cartridges from the magazine for the guns.
Boys aged up to 15 were designated 'Boys, Third Class'. Those aged between 16 and 18 were 'Boys, Second Class' who were in training to become seamen.
'Volunteers First Class' were gentlemen's sons sent to sea. They were a different class and hoped to eventually be rated as midshipmen, and eventually go on to take the examination for Lieutenant and gain a commission.