Back up question

Hi all,
Last October, I backed up my Mac to a WD Elements external hard drive. My question is, if I back up my Mac again, will the back up start from after I backed it up or will it back up all the info on my Mac again? I’ve searched everywhere and can’t find an answer. Any info would be greatly appreciated. Thanks in advance.

I back up my data one time in a month and checked that Mac Time Machine performs an incremental backup. It backs up new or updated data files with the name of the date of backup job creation.

Thanks for the reply and info.