TWRP is a recovery that can be used to flash firmwares on to the Samsung Galaxy Tab S. It can also be used for rooting the Tab S.
Here are the steps on how to download and install it on your tablet.
Play Store Link
1) Install TWRP Manager from the Play Store
2) Open TWRP Manager and provide root permissions
3) Hit Advanced->Install Recovery
4) Verify the correct device name on your screen then press Install Recovery if the correct device is showing
If you are not comfortable with the play store method, you can do a manual installation by using ODIN application. For that download the required TAR file from here.
Then in ODIN select the file by clicking on PDA button and flash it. Make sure you have your Tab S in recovery mode before pressing the START button. For getting your Tab into recovery, press volume up and power button down together as soon as the screen blinks blank so that it goes into recovery.