The 'Engineers' (Shown on the Galaxy map as a 'Purple Nut' symbol), will tweak various bits of your ship to make them perform better i.e. More effective/efficient weapons, shields or better FSD power plant etc. BTW If you're going to visit an engineer site DO IT IN SOLO NOT IN OPEN PLAY. There are sundry naughty people just hanging around such places waiting to relieve you of the hard earned goods the engineers demand as the price for their services. You can find the engineers and their requirements in your RH panel.
The modifications they make to your ship's machinery and weapons make the ship harder to kill by anyone intent on doing you in KP. You have to progress through the grades 1 - 5 and mods require various substances to be acquired to 'pay' for the modifications, ranging from elements surface mined on planets to more esoteric stuff like data obtained from interrogating ships by scanning them. Some of course just demand loot/credits but others want weird items from far flung places.
I suggest you buy an Orca (Which at c 400 mps flat out and a lot faster in boost can outrun most things out there) and do some passenger missions, they can be quite lucrative after you've worked up and become allied to various factions offering jobs, I reached 1.16 Billion credits mostly through passenger hauling, I've never mined a single void opal or cold diamond. But I vary it with a bit of combat at Res zones/nav beacons and elsewhere or do the odd cargo mission if the price is right. This afternoon I scored 10 million for just one passenger mission ... not as much as you'd get from hours mining away but it's a lot quicker return on your time.
My Orca 'Panty Raider' has no offensive weapons but is maxxed out on defence enhancements shield boosters, military bulkheads and a rated modules wherever possible.
I pack only 3 passenger cabins. 12 berth 1st, 6 berth 1st and a 6 berth business class. These 3 are more than adequate for any passenger missions offered. Don't bother with luxury class ... I've never had an offer of a job where it was demanded.