Hi I know you are just starting out so the easiest way for you to create it would be to create a primitive sphere and then create a new material ( say blin ) for it.Then select your sphere and hit ctrl +A on your keyboard to open the Attribute editor and go to the blin shader tab , then choose the colour you want it to be by clicking on the colour bar and picking it.Now you can play with the Incandescence, this will make the sphere give off light.To further enhance the effect you can go to the special effects tab (still on the blin tab in your Attribute editor) lower down and in that section is a thing called glow intensity, checkmark that and play with that setting to increase the glow.

There are other ways to achieve this ,but this is probably the simpliest way for you.

Goodluck ..