Turpentine is used to thin down the paint, in particular for under-painting or painting thin lines. Distinguish between turpentine and turpentine substitute (white spirit) which you use to clean your brushes and palette. If you find the small of turpentine too strong, you can use Low Odour Oil Painting Thinners instead. This does not smell nearly as much.
Because oil paint takes a long time to dry, substances such as Alkyd paint which is jelly like liquid can be used to half the drying time of oil paint. It also helps to spread the paint. Another drying agent is Gel Medium which is available in tubes.
There are many different mediums available on the market which you mix with the paint to either thin it down or make it spread more easily. Pick the mediums you prefer. The only two you really need are one for thinning and one to shorten the drying time of oil painting.
Gum Turpentine when distilled 100% becomes the most common solvent used in oil painting. Turpentine is usually distilled 2 - 3 times for maximum purity. Gum turpentine is not the same as wood turpentine. Wood turpentine is a by-product of the steam distillation of pine tree cuttings. Gum turpentine is from fresh, thick oleoresin collected from living long needle pine trees.