Starter's guide (Page 15 of 16)
Boarding a shipTo board a ship you will need a Marine officer and some marines. The amount of marines varies depending the size of ship you are trying to board. Some of the larger ship require upto 20 marines to board. Marines can be brought from recruiting officer, who can be found by asking -> Way to: Trader -> more -> more -> recruiting officer.
Once you have your crew, then you will need to disable your targets jump-drive and engines. Once done, right click on a ship and select board. The marines will then get into their space-suit and travel towards the ship. As the marines board you will need to help out by destroying the subsystems of a ship.
Hopefully with enough marines and some skill, you should capture the ship.