Fusion Genesis

Very easy and it comes very early.

After you complete the first segment of the game and are under the tutelage of Judah, he suggests you join a Faction to progress. The Consortium is the first suggestion he has, so just follow the white arrow to the base in the lower-right segment of the map, accept the mission and you're now a Trader!

To change factions or join a new one, go to Alpha station. Tell the guy you want to change factions. Exit the station. He will ask you which one you want to join. Pick this faction. Follow your quest marker. Finish the join quest mission (usually help someone in distress) and when asked if you want to join, select yes. Achievement unlocked.