What is function of the thinner?

Thinner is a solvent used to reduce the viscosity of paints, varnishes, and other coatings, making them easier to apply. It helps in achieving a smoother finish and helps in cleaning brushes and tools used in painting. Additionally, thinners can aid in the drying process by evaporating quickly, ensuring that the applied materials cure properly. However, it's important to use them in well-ventilated areas due to their potentially harmful fumes.