2. It will say that the device is busy if you current working directory is on the USB-device. Go to your home directory (cd ~), and then try unmounting it.
3. I assume you are using the command line, then the commands "mount /mnt/usb" and "umount /mnt/usb" should work, if the usb stick is set up in /etc/fstab.
You will need to add a line in the file /etc/fstab, mine looks like the following:
/dev/sda1 /mnt/usb vfat rw,suid,dev,noexec,noauto,user,async 1 2
Then you need to create the directory /mnt/usb. You will need to be root to do both of these.
Then, as a normal user, insert the USB stick, and issue the command "mount /mnt/usb", and your files will be available in the directory /mnt/usb. When you are finished, run the command "umount /mnt/usb" before removing the USB stick. When the command prompt appears again, you are safe to remove the device.
I hope this helps