A pure substance cannot physically be separated, and is made out of one atom (or molecule). Unlike a mixture, however, which are made out of two or more atoms or molecules. A solution in itself is the example of a mixture. (The composition of a pure substance being fixed, and a mixture's being varying depending on which.) And a solution branching off from a mixture into being either homogeneous mixtures or heterogeneous mixtures.
srry it kinda turned into a paragraph lol, feel free to add or take away anything :)