After doing research it said that nebulas are made of gas and dust. Are they actually gases and solids, or are they plasma?
Nebulas are not static objects - they evolve.
Initially a nebula might contain mostly (as an example) hydrogen, helium and some other elements in a cloud, but over time that material will clump together to form larger and/or denser material. Eventually parts of some nebula can even condense enough to form a star and it's planets. Our solar system was (probably) once part of a nebula.
So there's no single answer to your question. They can contain most forms of matter.