Noble gases are in group 0. This means they have a full outer electron field, this makes them unreactive. This also means they are monatomic - do not join with other elements that are the same, but are single and alone.
As you move down the periods, the gases have an increasing boiling point and also density.
Probably the most famous noble gas is Helium, as it is used in balloons. This is because it 'floats' due to the fact it is less dense than air, so rises above it, and is completely safe since it is unreactive. However, the densities increase as you go down the group.
In the above diagram, 5 balloons have been filled with the different noble gases, and then released from the same point. It shows where the balloons would end up because of their different densities.
Something else helium can do is make your voice become squeaky if breathed in. However, if you were to use one of the gas that are denser than air, the voice would sound deeper in pitch.
Neon is used inside those bright advertising tubes you see in Las Vegas for example. When a current is passed through the gas it glows a bright orange-red.
Argon, krypton and xenon are used in light bulbs of varying sorts and uses, all because they will not react from any heat produced by the bulb. Otherwise we would have exploding light bulbs.