I noted from the provided link that your device is a Samsung Light SGH-T399, running Android Jellybean 4.2.2.
With that considered, you can try the Framaroot app to root your device. Follow the steps below (guide in the link) to root the device. After rooting the device, copy the TWRP image to your internal SD card from your computer, and use the Flashify app (get it here or here) to flash it to your recovery partition. Again, the app itself will be pretty clear as to what you need to do, or follow the steps below.
Framaroot usage (from the XDA link (with corrections and emphasis)):
Download it to your device (links are available at the end of the linked XDA post)
Install it with a file explorer or directly from your internet browser, if android warn you about security risk, say OK and check Unknown sources to allow install of applications outside of Play Store.
Open Framaroot and select one of the following actions:
- Install SuperSU
- Execute script (for advanced users)
Possible cases once application has been launched:
A popup saying "Your device seems not vulnerable to exploit included in Framaroot", in this case you can uninstall app
You seeing one or more exploit name, also click on one after you have selected an action and you will see one of the above messages
Possible cases once exploit had been selected:
"Success ... Superuser and su binary installed. You have to reboot your device"
"Failed ... Exploit work but installation of Superuser and su binary have failed"
"Half-Success :-/ ... system partition is read-only, use local.prop trick. Reboot your device and use adb to see if it run as root", happen when the filesystem in use on system partition is a read only filesystem (ex: squashfs)
"Failed ... Try another exploit if available"
Framaroot crashed or foze, in this case relaunch Framaroot a second time and select the same action and exploit.
- Refer below screenshot. Tap on the "Recovery Image" button.
- Select the recovery image file you had copied to your decice earlier.
- Accept the confirmation dialog.
- You're done, reboot.
Flashify flash screen:
(image credits @cgollner of XDA,the Flashify developer)
Click on image for larger version
Reboot to recovery using
adb reboot recovery, the Flashify app or the key combination, configure TWRP time zone and other stuff, take a NANDroid backup and then go do whatever you want with the device, flash ROMs and whatnot.
If you are worried that the custom recovery may get reset after a reboot, you need not. That particular issue is only applicable to flashes via ODIN on certain select enterprise-class devices (and most probably yours isn't one of them), and has nothing to do with the suggested method.