Other than that its just minerals and systems.
Speaking of that, how does one use the systems they have?
First, unload them at a colony.
Then there are three possibilities:
1. Scrap them for 30% of the money and minerals that was used in building them.
2. Deconstruct them. If the parts use a higher techlevel than you have researched, you have a small chance of gaining a level. You will not get any minerals or money, however
3. Design a ship, using one or more of the components (alien components are marked with a (D) on the design screen).
When you build this ship and the colony, where you do this, has the components lying around (look at Economics --> Industry screen --> Stockpile) those components will be used.
Note: As those are _alien_ components, you can´t build them yourself, even if you have the tech to build them. So you can only build a ship designed with those parts, when you do have those parts laying around!