A sphere of fire is like a big ball made up of very hot flames. Think of it like a really big campfire, but instead of just being on the ground, it's surrounded by an invisible force field that makes it into a sphere shape like a giant bouncy ball. Inside this sphere, you would feel very hot and see lots of bright colors like red, orange, and yellow.
This sphere of fire is created by burning something like wood or gas, which releases energy in the form of heat and light. As the fire burns, it gives off gases that rise up and mix with the air around it, which can make the flame look different colors like blue or green.
It's important to remember that fires are very dangerous and should never be played with. They can spread quickly and cause a lot of damage. So while a sphere of fire might look really cool, it's not something you should ever try to make or touch.