Follow this link -- it walks you through how to enable the developer tab.
Show the Developer tab
As far as what all one can do with said enabled developer tab, that's more complicated. I've invested a lot of time learning this stuff, and have only scratched the surface. It has been almost 4 years and I'm still learning.
The benefit, though, is that by using it in combination with ASUTYPE (Although just recently I figured out a way I can create the same sort of functionality within Word itself, thus eliminating entirely the need for ASUTYPE), I can write an entire standard follow-up note in Word in about 45 seconds, then copy/paste it into AHLTA's, "Add Note", function. I save each note in a folder on my H: drive entitled, "FOLLOW UP NOTES", or whatever, using my self-designed naming convention so that each patient on my panel has a, "living note", on my shared drive. When I see them, I load the note in Word, alter as needed depending upon what happened during that encounter, then save the file with the changes before putting into AHLTA. This system does several things: (1) I always have access to the most recent note for every patient both locally and remotely via VPN, since everything is saved to the H: drive. (2) Static information such as diagnosis, allergies, previous medications tried, etc., is already present on the note, thus I have to only spend time on data that has actually changed since the last encounter (2) Negates any issues with AHLTA going down, as I still have access to my most recent encounter notes (3) I can tell you how many patients and every specific patient I have on my panel simply by opening the folder containing all active f/u notes and reviewing folder and file details (4) I can easily tell you the date of the last encounter with every single patient using file details in the archive folder, since windows timestamps the date any file was last modified; meaning, it was last modified when I saw them and saved the changes to the note. (5) This serves as a foundation to get really fancy if desired, using interoffice product functionality that allows extracting or importing data between Word, Excel, and Access.
Look up MS Word document automation and templates to get an idea of what you can do. If there's enough interest, I will even share my note template. Actually, my local IMD people saw my note template and had such a nerdgasm over it, they send a copy to Region. I never heard anything more about it, but I thought it was hilarious there was a perception that I managed to create a much better EHR system using Word and a network drive. For free. In my spare time.