Different things melt at different temperatures. Ice cream melts at quite a low temperature. That’s because it contains solid crystals of ice. It melts easily because when it gets warm the ice turns of water. If you heated it enough. the water would turn to steam, which is tiny drops of water, leaving behind just a gooey powder.
When a liquid gets hotter, more and more if turns to gas. Watch that happens to milk when it is heated in a saucepan. You will see little gas bubbles appear as it warms up.
Like water, most things in the world are solid when they are very cold, and melt to liquid when they get warmer. When they get very hot, they boil away to gas (like air).
Liquids have no shape of their own. They take the shape of the container they are placed in.