Matter is everything around us. It is anything made of atoms and molecules and it is anything that has mass and takes up space. If you don't understand mass, think it as the amount of stuff in an object.Matter can exist in 4 different states e.g. solid,liquid,gas and plasma.
Objects keep changing their states due to heat and pressure e.g.water can move in different phases like it changes to ice on freezing & ice can change back to water through heating due to evaporation.