Hy Sgt. G, I use the Nexus Root Toolkit but even in my opinion each of his device should supplie with a custom recovery or a custom ROM or a root access establishes all about it know what he does. Too long and too complicated, there is therefore not, but just too lazy to read!
Gave her the translated or only into German that also tried? I would say there is a mistake in the following place.
Installation TWRP Recovery1. you now Invite the TWRP V.22.214.171.124 down and copies it to C: \ Nexus72. The Image File open-recovery TWRP-126.96.36.199-flo.img renames her into twrp.imgagain follows 3. Now the command adb reboot bootloader4. The Nexus 7 will boot now in the boot loader5. Open the CMD C: \ Nexus76. Now the fastboot flash recovery twrp.img command follows7. appears on success writing recovery finished8. Back in the boot loader screen changes its with "Volume UP" in the new TWRP Recovery9. Now click on in TWRP "Install" so that the device drivers are installed