At this age toddlers are more interested in experimenting with paint than creating "artwork."
At this age, painting is a multi-sensory experience rather than a purely visual one. In other words, your toddler may be more interested in how the paint feels squishing between his chubby fingers than the finished "artwork." So prepare your clothing and surfaces for a mess (go outside if you can), and then let him go. Don't be surprised if your toddler shows more interest in the paint than the final product. Your toddler will explore the feeling of the paint in his hands: Is it slippery or sticky? Thick or thin? Does it splatter?
Provide craft sticks, sponges and brushes with fat handles that are easy for little hands to hold. Give him crumpled paper or a plastic bag to use as a stamp. Using these painting tools will allow your toddler to explore how paint works with different textures and surfaces.