While it is possible to manage your contacts in multiple lists inside your account, typically it is best to work with a single highly segmented master list. The reasons for this are :
- You don't run the risk of duplicate contacts across lists, thus increasing your contact volume
- You can save searches which will enable you to easily target and re-target certain demographics
- You can have up to 255 fields in one list, (with a maximum of 60 number field types) so you can segment in detail
- List and account management becomes a lot easier
Uploading a segmented list step can be found here.
The processes for uploading contacts can be found here.
Instructions on uploading into an existing list can be found here.