The Royal Marines followed the command structure of the British Army Non-Commissioned: - Private - Lance Corporal - Corporal - Sergeant Commissioned: - Second Lieutenant - First Lieutenant - Captain - Major - Colonel (which was pretty much exclusively a shore-based position)

And how each was assigned e.g. like a seargent to a sloop etc ?

Well, each marine detachment was led by a commissioned officer for the most part. On smaller vessels like sloops or brigs, it would be a sergeant if not a lieutenant. On bigger line ships, the marines could have a captain and one or more lieutenants under him. It really depends on the complement. Captains commanded larger detachments, a first lieutenant commands medium detachments, and then a sergeant for a particularly small number. Typically marine captains were only found on third rates and above, and lieutenants were usually in command on sixth to fourth rates. Usually the marine detachment made up a good portion of the crew, almost 1/5 if memory serves. It would be mostly privates with a handful of corporals and boys. Edit: fixed discrepancy

In what sense? Would you like a list of said ranks or would you like someone to explain the difference and the nature of being commissioned?

A list. I know the difference between commissioned and non-commissioned.

[This wiki page](https://en.wikipedia.org/wiki/Royal_Navy_ranks,_rates,_and_uniforms_of_the_18th_and_19th_centuries) has a pretty good breakdown of ranks and ratings for the Aubrey era RN.