We know that all matter is made from atoms and molecules. when a solid (the solute) dissolves ina liquid (the solvent), the atoms and molecules of the solute are able to fit into the gaps around the molecules of the solvent. When all the gaps are full then no more solute can dissolve. This is then called a saturated solution. When a solvent is heated the atoms and molecules have more energy and can expand more.
Heat increases the amount of solute that will dissolve.