Matter is any substance in the universe,from smallest dust to the largest planet.It has mass and takes up space.It can exist in SOLID,LIQUID or GAS.
Solid~~~ if a solid is put into containers of different shapes,the solid does not take the shape of container. This shows that solid has fixed shape.
Liquid~~ When water is poured into various containers of different shapes,it will take up the shape of the container.This mean liquid does not have fixed shape.
Gas~~Most gases cannot been seen.They occupy space and have mass.An inflated balloon show the air occupies space.Gas has no fixed shape.The shape of gas depends on the shape of the container.