Camden stretches out for about a mile along camden high street. Most people regard
Camden Town as all the stuff that lies between
Mornington Crescent (to the south) and
Chalk Farm (to the north).
The South bits of Camden Town are not all that special.. they contain many of the same shops you might find in any part of London, including the typical Burger King and McDonalds type stuff.
As you walk North-West things start to get busier - the streets get more crowded and narrower because of the market traders.
One of Camden's most interesting areas are it's enclosed markets - to the west of Camden High Street (Nearer to Chalk Farm Tube) you can find Stables Market - an aincient market now home to many trendy fasion boutiques.
To the east of the high street you can find the Canal Market - which is slightly less expensive but just as touristy.
As you leave Camden and behind you (walking north) and approach Chalk Farm look out for a number of good bars to your left: Bartock, and Lounge-jing are worth a visit. Also check out Marine Ices - an old Ice-cream parlour, and quite good pizza place.
Camden has a reputation for being a place to buy drugs - Whenever I walk around Camden Lock and the Markets I am often offerd Canabis. In my opinion, this is not a great place to buy gear. Camden is a heavily policed area that is rife with CCTV cameras. The chances are that anything you buy will be bogus. If not, the chances are that your purchace has been recorded on camera. My advice is that there are better places to buy drugs in London.
If you were to continue walking north you would get to Belsize Park and eventually Hampstead Village.