As you may have noticed, many of our tutorials cover topics that require you to have root access. When your phone is rooted, backing up apps doesn't require you to connect to your computer, and installing custom ROMs lets you get more useful settings. Rooting also lets you get rid of the Sense-style menus and status bar, and even upgrade to a newer version of Android.
Extract the Mini SDK .zip file to a folder anywhere on your computer, then copy the twrp.img file to this folder. I'll be using C:\sdk-tools. Now, copy the SuperSU .zip file to your phone, either with AirDroid or via USB.
Power off your device, then press and hold Power and Volume Down until you're in the bootloader menu. Highlight FASTBOOT and press Power. You should see Fastboot USB highlighted in red.
Open a command prompt on your computer and navigate to your SDK directory. Type "fastboot flash recovery twrp.img" and hit Enter.
On your phone, highlight BOOTLOADER and press Power.
This time, select RECOVERY and press Power to boot into TWRP.
Tap Backup and swipe to confirm. You can restore this backup if anything goes wrong by selecting Restore in TWRP's main menu.
In TWRP's main menu, tap Reboot. It will tell you that you're not rooted and ask you to install SuperSU, so swipe to confirm. When you reboot your phone, you should see a notification that you need to install the SuperSU app. Open the notification and select TWRP, since the app from Google Play only works with S-OFF.
That's it! For most people, the next step is installing a custom ROM or apps that require root. Be sure to check out some of our other posts on HTC One softModder for examples of some of the mods and customizations you can install.