Solids do not disappear when they dissolve in a liquid. You can get them back by evaporating the liquid away, leaving the solid behind.

When a solid dissolves, tiny bits of it come off and become part of the liquid. How quickly a solid dissolves depends on what you do to it.

Using small pieces of solid helps because there is a lot more of the solid touching the water than there is in a big chunk.

Stirring helps because it knocks bits off the solid into the liquid.

Making things hot helps break the bonds that link together the bits of the solid.