Warframe

Command is one of the Railjack specific skills. There are five total: Tactical, Piloting, Gunnery, Engineering, and for this achievement, Command. Each level gives you more bonuses to the given skill set. Command gives bonuses related to AI crew for your Railjack. These skills can be accessed through your Railjack menu or in the dock at your dojo.

You will need 1023 Intrinsics to take command to level 10. (According to the Warframe wiki.) You earn these points by earning affinity within Railjack missions.
Sera Di Siah pointed out in the comments that your AI teammates do not gain you affinity, so their kills do not contribute to your intrinsic gain.

Unless you have a skilled crew to carry you, your best bet will be to level any of the skills you use to around 4 or 5 so you can actually be useful in missions. (You only need 31 total to take a skill to level 5.) Then focus on command. Luckily this does not seem to be a very grind heavy achievement. There is another achievement in this update for playing specific Railjack missions, so it would be best to try to knock them out together.

The Crew
If you have a crew, you can use them to fill empty spots left by real players. The priority list is left to right on the crew screen. So the crewmate furthest to the right is the first to be replaced by an actual player, then the middle, then the left. Advise putting your engineer in the left spot to ensure you dont have to worry about repairs until you have a full crew.

You need to weigh how much of a hassle it is playing solo vs how much affinity you want. It may be wise to put 2 crewmates in as gunner and 1 as engineer and just reassign them (hold RB, press left on d-pad to pull up tactical menu and hit A on the characters gold icon above their name plate to pull up role selection menu) until you need the backup. Once reassigned your crewmate will stay at that station until reassigned again or the mission ends and they will revert back to their designated role.

The Boost
So, if you want to boost your intrinsics there are a couple of things you can do.
Smeeta Kavat can be modded to increase affinity gain.
Affinity boosters from the store will dramatically increase how many intrinsic points are rewarded with each mission.
Stealth farming using Ivaras prowl/sleep arrow to complete parts of the missions where you board an enemy ship or platform will provide a hefty boost to your affinity. (Remember to maintain that stealth multiplier.)
Currently the best boosting method is playing any Railjack survival mission.

The Railjack
Since this achievements centers around playing a lot of Railjack missions, it is good to know a few basic things about building up your ship.
First thing is your ship components and weaponry can be aquired one of two ways. First way is to research stuff in your dojo. These basics will get you pretty far and allow you to push through quite a lot of levels with the right crew and mods, but they are far from the best items you can get. They will also cost you a bit of resources and time. My advice is run up the ship components and pick a couple different weapons to level .All Railjack components and weapons have three tiers, Mk 1, 2, and 3.
The best items come from the second way you can get them and that is to find them in missions. These items will need to be repaired which you can do, but will also cost time and resources and usually be steeper than the dojo stuff you can research. Plus side is that these are more specialized in what they do so you can customize your ship to your play style. You can also combine non dojo railjack items to make them stronger.
Mods for your railjack will be found in railjack missions, do not forget to level and equip them just like everything else.

The you of it all
The last most important part of how you get set up is your weapons and frames. All frame abilities function just like normal. You will be using your archwing so if you like many others have avoided that part of the game like the plague, now is the time to dig in. Just be aware that railjack missions are functionally space battles with a regular mission to finish the node out, so it pays to know who and how your fighting.

Good luck. Anything to add, drop a comment.