Solvents are used to keep solid ingredients dissolved so they can mix with other ingredients.
There are 2 main types of solvents:
1. Polar (e.g water)
2. Non-polar (e.g chloroform).
Polarity is a chemical property that refers to the arrangement of charge around a molecule. Some molecules have charges distributed evenly around the molecule. These molecules are non-polar. Other molecules have charges distributed unevenly, e.g positive charges at one end and negative charges at the other, like a magnet. These molecules are polar.
Only polar solvents can dissolve polar substances, and vice versa for non-polar solvents. This is due to the different interactions between polar and non-polar molecules.