Answer and Explanation:
In saturated triglycerides structure, the fatty acids chains are composed by carbon-chains with single bonds between carbons. The chains can be aligned with each other and are more easily packed, thus the interaction strenght is higher. For that reason, saturated triglycerides are solid at room temperature.
By other hand, unsaturated triglycerides are composed by fatty acids which contain one (monounsaturated) or more (polyunsaturated) double bond(s) between the carbons and in consequence, the molecule bends. The bended chains cannot be packed efficiently, so the interaction strenght is lower and this kind of fats melt at lower temperatures.