Solutions are homogeneous mixtures of two or more pure substances. For our purposes, we will generally be discussing solutions containing a single solute and water as the solvent. What is a solvent? In crudest terms it is the molecule in the mixture with the highest concentration. That is to say if you had a liter of salt and 2 grams of water. In that case, the salt would be the solvent and the water the solute. But this type of mixture would be useless so why bother to make it??? When we do place solutes and solvents together, there is what we call the solution process. You can think of it as being similar to what you would experience if you tried to squeeze into an already packed elevator. Everyone has to adjust to "find their space" again. Now just like in the elevator, molecules will adjust differently dependent on the type of molecule making an entrance. And also like in an elevator there will come a point when no more people can be added. For a solution, this point is called the saturation point and the solution itself is called a saturated solution.