"Root" is the "page" that first open. If it's nothing to see on a USB stick or memorycard, no folders or anything, that's usually the root of the disk.
If the file you are going to use have to be in the root, just drag (or copy/paste) direct into the SDcard, not into any folder.
"Success is not counted by how high you have climbed
but by how many you brought with you." (Wil Rose)