Car will not start

For awhile the car was having a hard time starting, then it needed to be jumped to start. If I turned it off and tried to restart soon after, it would not start. Today when I went to jump it, it would not start, it just clicked (more than once). I do not know if it is the battery or the starter now. I do not want to put money into it unless I am sure. If you need any additional information, please ask. I want to get a proper diagnosis. Thanks so much!