What should I do with data and materials?

Since the latest update I collected a lot of "materials" and "data".

I found materials after destroying a ship and they often consisted of former parts of the ship, e.g. shield emitters or hull alloys.

Data was collected when I scanned other ships and in one case by finding a data beacon after following an Unidentified Signal Source.

These materials and data don't use any cargo space, but I don't know what to do with them. Selecting them in my inventory displays a message regarding engineers, but I haven't found any yet.

Where do I find engineers? What can they do with these materials/data?

If I don't want to give them my materials/data, can I sell them?

These are used in synthesis (in the cargo screen) and by engineers. When you get the engineers update you'll be introduced to a few of them, and then have to find others.

Synthesis lets you craft ammo and jump-boosts.

Engineers mod and enhance your kit for you, but it's a dice roll each time exactly how good it is.

Materials don't use up cargo, but annoyingly there's still a limit (600 I think) of how many you can carry.