In contacts, first name and last name are stored separately. If you need to import information which doesn't have the name fields separated out, the import process will do that for you. In your import file, specify a column title of "fullname" and the contents of that column are intelligently broken into the correct first name and last name parts. Allowable formats are:
Dr. John Smith (Dr. or other prefixes will be removed)
John Smith Jr.
Other variations may not parse correctly and will need to be manually corrected.