VOTE

http://www.fvap.gov/

 The website address above is the page for absentee voting.  Be sure to go there for further information. 

Voting is an activity of the 50 states.  The Consular Agency is a federal agency and can't register you or do anything except provide information and some forms.  The website above provides a link to each of the State Voting Departments so you can find out exactly how your state registers you or how you can get them to send you an absentee ballot.