Demystify reading DTC codes

[agaisin]

Hi - I'm trying to understand how to read various DTC codes.
At least 5 different ways to read different DTC codes and I'm trying to understand how they relate if at all.
1) toyota/lexus handheld tester
2) OBDII Reader/Scanner
3) Shorting out pins on the DLC3 (same as OBDII connector under driver's side by the right foot/gas pedal)
4) Service Check Mode (either hitting Display and top left bottom left 3 times within the screen or holding info and flicking on/off the headlights 3 times) - you can navigate through various screens and in LAN Monitor you can see DTC codes
5) car off, hold down auto and recirc button and then turn key to ON, you'll see DTC codes where the inside temp is normally displayed

- I assume with the handheld testers from toyota you can see everything. No need to do any of the others.
- What can/can't you see with an OBDII reader?
- When do I need to short the pins to see DTC codes?
- Is the Lan monitor just for seeing AVC lan DTC codes?
- Is the auto and recirc just for ac related DTC codes?
- Are there other ways to read DTC codes?

Thanks!
Art