(Tip) The ABSOLUTE FIRST THING you need is the Tactical Navigation System - without it you're just blundering around in the dark. So your first goal is to get 500 spare credits so you can proceed to the Trading Station and have it installed.
(Tip) Press 'H' to get a display of the commands.  Warning: it's not complete, but it's better than trying to read the manual!
Pick a station, hit 'T' to get your radar scanning, then head for it until your radar locks on.  The lock-on message will tell you what kind of station it is.  Press 'I' for an information display that will show you what that station buys and sells.