How do I find civicrm field names for import?
When importing memberships the type needs to match name of the type from the first column on the membership page (Administer => CiviMember => Membership Types).  So if you've defined a membership type of "Gold Member" then when importing, you need to put Gold Member in the column for membership type in the CVS.

Importing relationships is a bit trickier.  You can only import one type of relationship with each cvs file.

Have you looked at the on line book on importing.  It gives some good examples and tips on importing.

http://gitbook.civicrm.org/common-workflows/importing-data-into-civicrm.html