Difficulty:
EasyYou can see Merchants both on the game map, or out and about visiting stations. While looking at a nearby merchant press
to hail the merchant and then threaten them to drop their cargo.
This doesn't always work and you will have to fight them if they refuse.
In my experience, the bigger and more powerful your ship, the more likely they are to pay up.
Note: If you struggle to catch up to a merchant then you can head to the station you think they're travelling to and wait, or look for a mission involving mining, or defending miners, as these usually have merchants in the area.
Note: Shooting a merchant will cause them to attack if you inflict significant damage.