A little terminology nitpicking, but might help down the road to make things clear. The chainring is just the 1 ring with the teeth on it. You have 2 chainrings. The entire assembly (2 chainrings, plus crank arm) is called a crankset (or chainset in England).

Your 6 speeds in back is a freewheel, and threads onto the hub. More modern bikes have cassettes, and range from 7 - 10 cogs and the cogs slide onto the freehub and are kept on with a lockring.

Now, do you need a new crankset ? Or just 1 chainring ? What was the reason given ? Cranksets usually last a very long time.
If you post pictures of the parts, it will help determine what you have & what you need.