Solution

We should wear cotton clothes and light coloured clothes in summers. We sweat a lot in summers. Cotton is a good absorber of water. Thus, it absorbs sweat from our body and exposes the sweat to the atmosphere, making its evaporation faster. During this evaporation, particles on the surface of the sweat gain energy from our body surface, making the body cool. Further light coloured clothes are poorer absorber of heat and would be better for summer.
The key to this answer is evaporation and the property of evaporation that it causes cooling. Link evaporation to the types of clothes.