Mixtures can be categorized as heterogenous or homogeneous. Heterogenous mixtures do not appear to be the same throughout. Concrete, granite, and oil and vinegar are all heterogeneous mixtures. The particles are large enough to be seen and can separate from the mixture. Homogeneous mixtures are very well mixed.
Solutions are homogeneous mixtures.
In a solution one substance is dissolved in another. The particles in a solution are atoms, ions, or molecules. The particles are obviously too small to be seen and will not separate out on standing. Solutions have two parts. Water is a solvent which can dissolve 1,000s of substances.