It isn't usually necessary to back up your entire photo and documents folders if you do it on a monthly basis. This being because you'd probably only be backing up folders and subfolders that have already been backed up. Normally, it would only be necessary to add photos/documents/files to the back-up that have been saved to the computer during the past month. However, if it's been a year since any backing up was done, then it might be best to back up all created files on this occasion.
There is back-up software available for the job if you want to use it, including that within Windows itself. This can be set up to back up chosen folders automatically once a month (more often than that if you want). I've never used software for backing up though. I usually manually copy any files/folders to another drive in order to back them up. There are a few ways it can be done but perhaps the one described below would be the easiest. It will work with all files/folders (documents, music, photos, videos for instance). I'll use a photo folder as an example:
* Make a new folder on the external USB drive. Use the current date as a name for the folder.
* Go to the C: (main) drive and right
-click on your photos folder and choose 'Copy' in the menu that opens. This will copy the folder and any sub-folders within it to that mystical area called 'The Clipboard'.
* Now go to the new folder that you created on the external USB drive.
-click on the folder and choose 'Paste' in the menu that opens.
* The photos folder on the C: drive will start to copy into the new folder on the USB external drive (a progress bar appears that shows the files copying).
* When done, open the folder and the photo files should be visible there.
The best thing to do is experiment with some photos and folders that don't matter until you are comfortable about making the operation work as it should do.