Does a solution have to involve a liquid? explain.

No, not always. There is always going to be solutions of gases in the air. And, there may be a solution of metals in alloys.

Basically, a solution is just any of the same mixture, which is solid-solid, liquid-liquid, and gas-gas.

Yes a solution does have to involve liquid. For example. when when dissolving a solid you must have liquid to do so. And it also must contain liquid for another liquid. The Fact f one substance dissolving into another substance will require liquid.