When you click on the Upshift icon, it will pop up a list of new addresses that you can select, which all go increasingly higher in the address of the site you are currently viewing. You can use shift+click to open the address in a new window, or ctrl+click / middle mouse click to open the address in a new tab. There is a keyboard shortcut, ctrl+up, that allows you to go up one level in the current address. Upshift does not use your data for any other purpose, or save or send anywhere.