Oil Paint
When you are working with oil paints it is important that you keep the brushes clean so that the fibres do not splay and the brushes remain useable for many years. If you buy quality brushes then they can be quite expensive and therefore you need to spend time cleaning them so that the money you have spent is not wasted.
Most people tend to clean brushes that contain oil paint with thinners or a turpentine based solvent. This is effective but some people are not keen on using this as the smell can be quite overpowering and also this requires special disposal as you cannot normally throw turps and the like down residential drains.
However, there is a way to clean brushes that you have used for oil painting without using thinners or turpentine. If you get some basic soap or some washing up liquid then you can use this instead. Rinse the brush with warm water and rub it into the soap. Use your fingers to work the soap into the brush to remove the oil paint. Keep rinsing the brush out and soaping it so that you remove the soap and the paint each time. Keep doing this until the paint is out of the brush. As long as you use warm water this should work quite well.
Acrylic Paint
If you use acrylic paint then the main thing to remember is to wash the brushes as quickly as possible after you have used them, or at least put them to soak in some water. When acrylic paint dries if becomes a kind of plastic and it is impossible to get out of the brush as it is no longer water-soluble. So you can just use water to clean your brushes with but do it quickly!