Light is a kind of energy called "electromagnetic (EM) radiation." Radio waves and microwaves are at the low energy end of the EMS while x-rays and gamma rays are at the high energy end. The part we can see is "visible" light, and it's right in the middle of the EMS in terms of energy. Light travels fast (About 186,000 miles per second [300,000 kilometers per second],) and in straight lines.
What Creates Light? When electrons collide they transfer energy! What does that have to do with light? Imagine this - you bump into the guy standing next to you and spill hot coffee onto him. On impact he enters a higher energy or "excited" state, after which he wipes off the coffee, calms down, and returns to normal. (Yes, it's a weird analogy but stay with me here). Atoms slam into each other all the time, but instead of spilling coffee on each other they transfer a little energy. The receiving atom goes into an "excited state" where its electrons briefly jump to higher energy levels. When the electrons "calm down" they release the extra energy as photos (packets of light) and return to ground state.
No two elements produce the exact same "light" (spectral) fingerprint so by looking at a bright line spectrum scientists can tell which elements are in a gas sample or star.
These resources will give you a better appreciation for light and the EMS:
Physics4Kids: Nice, easy overview of light! (Be sure to click through Overview, EM, Visible and Structure).