When you flash TWRP with Odin you have to reboot immediately in recovery as if you reboot the systeme TWRP will be overwritten by the stock recovery.
To achieve this when in Odin untick "AutoReboot" and flash TWRP.
When the the flash is finished power off your tablet : long press on Pwr button till it goes off.
Then reboot in recovery mode: volume up, home and power you should be in TWRP recovery.
I am now have problems with s-pen. Is this connected to the root process? I can write with my hand but not with the s-pen. Do you have any idea what is happening?