Its a good idea to separate your People list in to the different types of customer that you have. This not only helps you when you want to report on the different groups, but also allows you to potentially set up different templates for each of them in the future.
You can set up one main segment for each customer. When you're adding your customer - choose the People tab up the top, and the click "Add Person". You will have the chance to select the segment you want to add them to, or add a new segment on the fly by just selecting "Custom" from the Segment drop-down list.
You can also set these up with a CSV file. Just add the column that you want to segment by, and then make sure when you're importing the file that you map that field to "Segment".
If you need some help getting your CSV imported, have a look at our article on Importing customers.
Custom Data fields
These are awesome for when you have even more data information you want to add about each customer. You can have as many custom data fields as you like; just add these columns to the CSV file you're importing. Much like the segment, when you're importing the file just select the Custom Data "Import as:" option for each column.
What can you use these for?
You can use these however you like! Some people like to break these up by location, account manager, type of customer, Industry - the possibilities are endless!