A Person Account is a special type of account. In the underlying database, they are represented as an account and a contact, but in the UI they will appear as one record with its own unique layout. The distinguishing feature of a person account is its "record type." An account with a Person Account record type (also, the IsPersonAccount flag set to true), is a person account. This simplifies reporting, because you can report on them as accounts or contacts, and you can use them anywhere you could use an account or contact (such as lookup fields, etc). The specific value that will be held in the lookup field will match the ID for the type of record it is; account lookups will use 001... and contact lookups will use 003... Of course, there are certain limits as to what these accounts may do, but in general, they behave as the appropriate record for whatever type they need to be. No new object will appear, but the metadata for objects/Account.object will change to reflect the new record types and fields, and layouts/*.layout will add new layouts appropriate to the the new record types.