For oil painting, it is necessary to choose good colors, as well as brushes that  vary in sizes, and then, choose a picture you want to portray, and then. Paying attention to the movement of your subject is important for planning your brush strokes. Realistic paintings have brush strokes that create movement. Try mixing colors to get a better effect, and always survey the effect, to prevent strocal mistakes. For oil paint to dry completely, it may take up to 3 months, even longer if your painting has many thick layers of paint. Put your painting where it won’t be disturbed or damaged and allow it to air dry for the necessary time. Then for a shine, varnish it, Ta - Da!!!! your awesome oil portrait is done!
If you have colour, you should mix them with oil
Both powdered or paste form is avialable in market
After mixing, you can apply them to paper
use willson and newtons colours in oil paints