The difference between uniform and non-uniform mixtures is the degree at which the materials are mixed and the sameness of their composition throughout the mixture.
Another word for a uniform mixture is a homogeneous mixture. Homogeneous mixtures have the same composition throughout (home = the same). There is only one phase (state of matter) observed in a uniform, homogeneous mixture. By definition, solutions are uniform/homogeneous mixtures. Examples would be Kool-Aid, fruit punch, salt water, vinegar, vodka, etc.
On the other hand, non-uniform mixtures are also called heterogeneous mixtures. Heterogeneous mixtures are not the same throughout (hetero = different). Trail mixes and salads are great examples of non-uniform, heterogeneous mixtures. Every handful that is grabbed or bite that is taken is slightly different.