Note the companion will not look like mine till you configure to, but that's completley up to you.

Follow the instructions on the main page of Fallout 4's nexus site, on how to install plugins.
http://www.nexusmods.com/fallout4/

Install Samantha Companion.

Place both the batch file and the esp into your Fallout 4's Data folder.

After you have configured your plugin.txt file, launch the game.

Once in the game you will want to type set SamanthaFollow to 1.

When she appears open console by typeing ~ then type bat F4followers then enter.

Next in order to change the appearance of the npc type slm + your character's i'd located in the console window.

Samantha's Base ID is as follows 0157774D, you can spawn multiples of her and change them as you wish, but once the game is reloaded they will be clones.

To do this you type Player.placeatme 0157774D (amount of followers you want or don't type anything)