Turpentine is a solvent which is used with oil paint to dilute the paint and wash brushes. Oil paint can not be mixed with water so solvents like turpentine and white spirit have to be used, or do they?
There are now alternatives to using turpentine. Turpentine and other solvents such as white spirit have strong fumes which are not nice to be around. In some of my art classes a few students have left the class complaining about the fumes. There is the option of odourless turpentine which improves the fume smells but it is still harmful to breathe in.
If you do buy turpentine then I would recommend buying artists turpentine from an art store rather than the sort you get at DIY stores. It is just a bit more refined and easier to use with paint.
So what are the alternatives?
There are alternatives to turpentine. You could use water-based oil paints which would mix with water. These paints are in my opinion just as good as oil based oil paints.
You could also use non-toxic linseed oil which has been used in painting for centuries. Linseed oil has a mild odour and will loosen up the paint and thin it so it can be applied in smooth brushstrokes. Linseed oil is more expensive than the turpentine but well worth it if you don’t want to breathe in fumes and dislike the smell of solvents.