where to exactly view to the files of a mounted usb.there are many folders when i left click usb icon on left of my filemanager home page like sys,selinux,mnt,usr,dev,tmp .....and each folders consists different other folders .where to view the files of a usb like photos,songs etc.{please give the exact path!}
thanks

I always just mount manually to prevent this sort of confusion:
This puts the first partition on the USB stick under /mnt

Check the block device being assigned by plugging the stick & running `dmesg|tail` in a terminal.

If you're using the Thunar file manager, it shows up in the side pane as a USB stick (if you have auto-mounting enabled) -- I think this is also true of most other file managers.

Most usb devices will be found under /mnt or /media.

Not sure what you are looking at, or what system you are on. When you stick the USB device in it is usually automatically mounted at /media
If you are looking under 'filesystem' from a file manager you are sort of 'jumping the gun'.
Without knowing what desktop you are using, and there are many, go to a terminal and type mount, it will tell you what is mounted. The USB device will most likely be listed as /dev/sdb1 with a mount point (/media/the name the device). This is a long way around.
The GUI you are using will be more simple, eg, Places me , me being the name of your home folder and in there should be something like "New Folder", or even an 8 digit record, that is your USB.

Fred.

or on newer systems
/run/media/YourUserName/"uuid" number
but it should always show up in the "places" pane in the filemanager