I live in a pretty hot climate, but it’s only really unbearable at times due to shoddy building and bad urban planning. Even then, summer can be difficult.
I can’t imagine what it’s like on the equator, especially in dense urban centres. What’s Mumbai, Bangkok, or Singapore like at the height of the wet season?! How do millions of people function day to day?
I was born and raised in Las Vegas. It’s a dry heat so water helps. I soak my shirt or hat and I can be outdoors for a while. Loose fitting light colored clothes and a wide brimmed hat go a long way. Stay in the shade or go out at night. Drink plenty of water, this is the biggest thing.
Indoors, a fan can help. An evaporative cooler is very effective in the dry heat. We’re spoiled so most places are air conditioned, so I try to go places that are free to be in like the mall, library, grocery store.