[Galaxy Tab S Q&A, Help & Troubleshooting] Southern_Comfort:
Don't fret. I am a total noob too. I got the following information from a different site, Unfortunately I cannot post the link as a noob. Once I have enough post count, I will add the link to the source (fairness to the author of the source).

How to flash Samsung Stock Rom using Odin

Home > Tutorials > Last update on February 1st, 2015

These are the instructions to flash Samsung Stock ROM (original firmware) using Odin on Windows Computer.

Requirements: Your Samsung device should have at-least 30-40 percent of phone batter to perform the flashing process.

Flash Samsung Stock Rom using Odin

Step 1: Download and install Samsung USB Driver on your computer. In case you have already installed the Samsung USB Driver on your computer then Skip this step.

Step 2: Download (Stock ROM compatible with your device) and extract it on your computer. After extracting you will be able to see these kind of files:

T800XXU1ANJ6_T800XAC1ANI1_HOME.tar.md5

Step 3: Now, Enable USB Debugging on your Samsung Galaxy Device. To enable USB Debugging: Open Settings > Developers Option > USB Debugging > Tick to enable.

(Developers Option is hidden for Android 4.2.2 or above, to show the developer option Go to Settings > About Phone > Built Number (Tap on it for 5-8 times).

Step 4: Power Off your Samsung Device.

Step 5: Now, you have to boot into Download mode. To boot into Download Mode: Press and Hold Volume Down Key, Home Key and Power Key. When phone vibrates Leave the Power Key but Keep holding the Volume Down Key and Home key. You will boot into the Download Mode.

Step 6: In the Download mode you will be able to see a Warning Yellow Triangle Sign. In this situation you have to press the Volume up key to continue.

Step 7: Download and extract Odin on your computer. Use Odin 1.85 (Successful in downgrading to KitKat from Lollipop)

Step 8: Now, Open Odin3 and connect your phone to the computer.

Step 9: Once you have connected the phone to the computer, Odin will automatically recognize the device and show “Added” message at the lower-left panel.

Step 10: Once your device is detected by Odin, click on the “PDA” (or AP) button and select the tar.md5 file that you have extracted in Step #2.

Step 11: Now, click on the “Start” button in Odin to begin the Flashing process.

Step 12: Once you see, the Green Pass Message then remove the USB cable from the device (during this process, your device will restart automatically).

Step 13: Your Samsung Device will now stuck at boot (boot loop). Now, You have to boot into Stock Recovery Mode, To Enable Stock Recovery mode: Press and Hold Volume UP key, Home Key, Power Key. When phone vibrates Leave the Power Key but Keep holding the Volume UP Key and Home key. You will boot into the Recovery Mode.

Step 14: In Recovery Mode, Wipe Data/factory reset.

Step 15: Once Cache Data is cleared, Select Restart Phone Now from the recovery menu.

Step 16: Now, your Samsung Device will restart without any issue with the Stock Rom you have flashed.

I ran into problems flashing the ROM twice and I went into a complete panic (could be Odin 3.10, or corrupted ROM). My region is XAC. Initially I tried XAR, and failed miserably. Eventually I downloaded the XAC ROM from a different source (SamMobile), also using Odin 1.85 instead of 3.10. Everything went smoothly (with the above stated boot loop). Should you get a Fail message in Odin, use the instructions from droidviews (do a web search on droidviews and "firmware-upgrade-encountered-an-issue-solution". Again, I will post the link once my post count is slightly higher.)