You have default permissions to write and create folders in your home directory. You do not have default permissions to write or create folders anywhere else.
You home folder will be found at /home/username/ and most applications like LibreOffice will default to here, or possibly /home/username/Documents
With a few exceptions it's a bad habit to get into writing elsewhere in the filesystem for just data. These special cases are set up with special permissions and are for specific purposes - eg /media/username.
If you are having problems writing to your home directories or creating folders in them then it might indicate that there is a permissions problem which needs to be addressed.