What is a comet ?
A comet is a object which is made up of things water, dirt, frozen gases like methan. Think of it like a dirty snowball.
Comets were formed a very long time ago.
Comets are thought to come from a belt of objects called the kuiper belt..
Comets are usually seen when they get close to the sun. As the get close to the sun, they are heated up by the sun, causing the material to come off the comet. As the material comes off the comet, it forms the tail of the comet. The way the tail appears, depends on how close the comet is to the sun, as the solar wind made up of particles from the sun, influence the shape of the tail.
Depending on the material that the comet is made off, how close the comet gets to the sun and other things, will determine how bright the comet gets.
Comets travel in orbits around the sun. Some comets take millions of years to orbit the sun, while other's take just a few years.
For example a comet called encke takes around 3.3 years to complete an orbit of the sun. While a famous comet called Haley, talkes around 76 years to orbit the sun. Then there is one's like Hale Bopp, which won't be back for a very long time, a once in a lot of lifetimes comet.
How to view a comet
Depending on how bright the comet gets, you can see it in a telescope, a pair of binoculars, or just with your eye.
You need to know where to look in the night sky to see it, there are websites, and astronomy software that can tell you that info. You also need to have a orbital elements for the comet, which is data on how the comet orbits the sun.
Here are some sources for the orbits of comets.
Web Sites on Comets
Comet Observation Home Page