You see, stars are huge balls of fire. They aren't just any fire. That fire is from a constant number of nuclear reactions. Not all stars have solar systems spinning around them. Some stars are just sitting out in the middle of nowhere.
Some stars have a companion star nearby, kind of like a twin.
A star is a huge ball of plasma, usually made of Hydrogen and Helium. That ball of fire also gives off light. All kinds of light. There are visible, IR, UV and X-rays constantly being broadcast into space. You may find planets that are almost identical to the makeup of stars, like Jupiter, but something has not ignited their nuclear reaction.