oils have lower melting point(gingely oil) hence remain as oil in winters. please explain it

Saturated fats have high melting points and they are solid at room temperature. Saturated fats have no double bond between molecules  since their carbon skeleton lay very nicely on top of each other hence they have somewhat stable structure.  E.g. butter, Coconut oil, tallow, suet etc.
 
While unsaturated fats are liquid at room temperature. Unsaturated fats have single or multiple double bonds in tandem. Due to these bonds, the successive layers of unsaturated fats are not able to properly align over the adjacent layers hence they usually have low melting points and they always remain liquid in low temperatures (around zero degrees) and room temperatures. E.g. olive oil, peanut oil, sunflower oil etc.

Regards