lsblk to find the device name of your usb device. Naming is /dev/sdXY. Where X is any english letter and Y is integer, typically 1.
If the device was mounted, you will see the mountpoint, for example:
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sdb 8:0 1 15.2G 0 disk
└─sdb1 8:1 1 15.2G 0 part /media/me/4C45-110F
If not, mount it. Follow to the step #3
udisksctl mount -b /dev/sdXY , device name same as in previous step. (/dev/sdb1 in my example) The mount folder will be reported back to you to use in the next step. For example, suppose lsblk tells me this:
sdc 8:32 1 7.5G 0 disk
└─sdc1 8:33 1 7.5G 0 part
Then I will do the following:
$ udisksctl mount -b /dev/sdc1
Mounted /dev/sdc1 at /media/xieerqi/A669-34EF.
You can see it automatically created /media/xieerqi/A669-34EF folder and mounted my pen drive there. Also , big advantage is that you do not need sudo.
Use rsync or cp or mv to get your files to the folder reported in step 3. Consult manual pages on usage of these commands. cp and mv are simplest. mv FILE DESTINATION - in my example
(where FILE is the thing you want to move to the drive)
mv FILE /media/me/4C45-110F
rsync is the best for backup however.
For example, to backup TESTDIR to my usb drive, I can do this:
$ rsync -av /home/xieerqi/TESTDIR/ /media/xieerqi/A669-34EF/~
sending incremental file list
created directory /media/xieerqi/A669-34EF/~
sent 228 bytes received 125 bytes 706.00 bytes/sec
total size is 0 speedup is 0.00
NOTE: some drives mount to directories that have names with spaces. If you run rsync or mv with not quoted names like that, your data will not be copied to correct destination. Always quote pathnames that have spaces in them.