Answer to Question 1
Sunlight filters down through the clouds and warms the surface, but heat cannot escape easily because the atmosphere is opaque to infrared radiation. Traces of sulfur dioxide and water vapor help trap the infrared, but it is the overwhelming abundance of carbon dioxide that makes the greenhouse effect on Venus much more severe than on Earth.
Answer to Question 2
Volcanism around the ring of fire is caused by the motion of the tectonic plates, and are composite volcanoes. On Venus, there are no plate tectonics so the volcanoes are shield volcanoes, the type produced by hot-spot volcanism.
