car wont start

i dont know anything about cars so i need a little help i tried to go to work this morning and i started my car as usual and it started for about 3 secs and seemed fine but died so i try again but doesnt start... i have no idea wants wrong it seemed fine the night before and now when i try to start it all i hear is a clicking and my lights are dim, do i need a new battery? or is it the starter?