I'm a little confused under the Tactical Marine's starting compliment of skills it lists getting Command as a trained advanced skill.

But Command is a basic skill... and all Marines have it already...

So... what's the deal?

marines are not trained in command, but yes, it is basic, not advanced. this means tac marines by default can make command tests at their full fellowship, instead of 1/2 fellowship. also, it means they have an advantage as squad leader, providing a higher cohesion pool.

I get that. But what I'm unclear on is the word "Advanced". Does that mean advanced in the sense of the skill I'd have if I purchased the +10 advance at Skill Level 2... only I get it at skill level 1?

5-9's of certaint it means you start with it as 'trained.' You tick that extra box and get to use your full fellowship when making test, not +10 or more to your roll.

The "advanced" is more than likely a typo due to a copy paste error from other classes like Librarian and Assault marine, who get Psinicience (yeah, that can't be the right spelling) and Pilot (Personal), which are advanced skills.

Advanced is a typo, since Command is not an advanced skill. As Charmander said, just check off the trained box on the skill. Later, when the character has access to buy the command skill (rank 2), a tactical marine does not need to (nor is even able to) buy the regular version of command. The regular command does not turn into a version of command +10 to buy. The character will need to wait until rank 4 (unless an ultramarine) to purchase command + 10.