It's electromagnetic energy.
The speed that it travels if the speed of light (since it is a form of light, or more correctly, visible light is a form of electromagnetic energy)
The frequency is the rate at which the magnetic field and the electric field go through a cycle of changes in polarity.
Since it has a speed and something is changing regularly, we can measure the distance try it travels whilst doing a cycle. This is the wavelength.
Imagine that you are on a train playing with a yo-yo. One cycle of the yo-yo is from when it leaves your hand to when it returns. Let's say you can do this about 144 million times per second. Let's say that your train is an express which always travels at the speed of light. The train, and hence your yo-yo will travel about 2 metres for every cycle of your yo-yo. It has a wavelength of about 2 metres. Your yo-yo is on the train for as long as it's on the train, and it keeps on yo-yoing for as long as you yo-yo it. The wavelength is just a relationship between frequency and speed, it doesn't limit how far it or the train goes.
