The rooting phone will erase all of your data.
All described operations you are doing at your own risk.
If want saves your data do a backup before start.
The battery should be at least 50% charged before starting.
To start root process first need to turn on OEM LOCK option from Developer settings, without this can't do anything.
(if the SAMSUNG N900A Galaxy Note 3 LTE (AT&T) does not have this option just ignore this information).
That all your SAMSUNG N900A Galaxy Note 3 LTE (AT&T) rooted without any problem. Congratulations.
If you want to be sure that device is fully rooted best uses application from Google Play Store like Hard Root Checker. Install it and enable and you will have information about Root and Busybox status. Simple but very helpful.