What was the energy at the start of the universe and how did it create matter? As for how it became matter, that’s “easy”: when you get enough energy in one place, new particles form spontaneously. Newly created matter is a random assortment of all the fundamental particles it’s possible to create at the given energies. So that’s ultimately the answer to what kind of matter we can create: protons, neutrons, and electrons (and their anti-particles). If your spaceship is big enough to hold a black hole for power and a couple massive stars for fusion, then you can create oxygen.