In the dark grey band you'll see "+ Add new profile", click this. Select the radio button to add a profile to an existing domain and give it a name. Once you've saved it you're redirected back to the settings page, but now you'll see your new profile in the list.

Now click "Edit" on the far right, this will take you to the profile settings page. Here you can change all your standard Analytics settings for each profile. The most important aspect here is to edit the profile filters. Click "+ Add Filter" in the grey bar in the filters section. Leave the radio button on "add new Filter for Profile" and give it a name.

At first stick with the predefined filters. Here you can choose to include or exclude traffic to specific areas of your site, from certain domains and IP addresses. If you want to look at traffic to a specific area of your site select "include only" from the first drop down menu and "traffic to the subdirectories" in the second. Depending on the structure of your site you'll have to give the third some thought. Then simply enter the subdirectory and save.

If you've got the skills and time to delve deeper into the custom filters you can create some very powerful profiles, for instance you could focus on traffic from a specific geographical area to a specific subdirectory.

Tip: Don't forget the add conversion goals to your new profiles.