Most of the heat on Venus is due to the peculiar heat-trap its atmosphere provides. On Venus, intense sunlight filters through the clouds and heats up the rocks on the surface. Instead, its energy is trapped in the atmosphere, adding to the heat provided by sunlight. Ordinary window glass behaves in much the same way on Earth as carbon dioxide does on Venus. Imagine a car parked in a sunny parking lot with the windows rolled up.
Sunlight gets through the windows, and warms up the car's interior.
In a way, Venus can be thought of as a car that's been left in a sunny parking lot for four billion years with the windows rolled up. Temperatures will range from the low to high 900s, Fahrenheit. Compared to Venus, the Sahara Desert is like a swamp. Under the clouds, on the surface of Venus, daylight is hazy yellowish, and about as intense as it is on Earth during an overcast day. Also, if someone on the surface could see up through the clouds.