Tablets and phones are not really meant to connect to USB devices. Also, phones and tablets are not meant to connect to each other.
If you have access to a computer, the simplest way is to put the files on a computer, from the flash drive, then connect the tablet to the computer and copy or move them over to the tablet.
Now if your tablet doesn't have internet access, but your phone does, you can try using the phone as a hotspot so that you can download any files to the tablet directly. Instructions bellow. However, to be honest, the fastest way is to move files to computer and then move from computer to tablet.
If it is at all possible it would be done this way...
Go into "Settings" and in the "Wireless & networks" section tap "More".
Now tap "Tethering & portable hotspot".
For "Wireless Tethering" tap "Set up WiFi hotspot"
On this new screen you will see options for a "Network Name", "Security", "Password" and "Network Band". You can change them or keep them as is. It is really up to you.
Now you would just need to search for the hotspot by name using the second device.
NOTE: While a WiFi hotspot feature is built into Android, some service providers/carriers, especially in the United States, hide it. You would then need to see if you can locate an app that you can install to help with this.