If you want to root your Android device, or install custom ROM, you need to know Kernel version, Baseband and Build Number of your phone. ON HTC One you need to do as follows to get this information
1. Open "Settings" app
2. Scroll down and tap "About"
3. Tap "Software Information"
4. Tap "More" to see Kernel Version, BaseBand version, Build Number, and Browser version