Not sure if serious, but your question is too vague. A space company can be someone who develops software for satellites. Maybe someone who develops a small sat

Not sure if serious, but your question is too vague. A space company can be someone who develops software for satellites. Maybe someone who develops a small satellite itself. There are many niches in space. The now what? depends on what you pick. Now, if you want to build spaceships, then you might want to apply for a job at NASA, Lockheed, etc. See what it takes to go to space and learn from what they are doing.