More complex solutions contain one solvent and several solutes.
There are as many types of solutions as there are possible combinations of the three ordinary states of matter. By far the most common solution encountered in the lab is the aqueous solution in which water is the solvent and some solid, other liquid or gas is the solute.
So just what does it mean to "dissolve"? In the most general sense dissolving means that two or more phases merge into one and all of the various components become evenly distributed in the mix--in other words, the mixture is homogeneous. In many cases this change is clearly visible.
Exactly how dissolving happens will vary depending on the nature of the components. Since the most common type of solution we use in the lab is a mixture of a solid in water, a closer look at that situation may shed some light on the general process.