We heard once that in the 4th millennium B.C. some guy asked the person who invented the wheel that question. The person who invented the wheel’s answer, we were told, was something like “well it’s not actually that simple - it required engineering and innovation and this thing called mathematics that probably hasn’t been discovered yet and blah blah blah…” on and on and on until the guy got called away to go fight a minotaur or something.
Cool story, right? We mention it because stacking headers are sort of like the wheel to the Arduino civilization - meaning this thing that’s incredibly simple, incredibly useful, but still so brilliant you’re amazed they didn’t exist before the day they started existing.
Some experimentation might be necessary to get these working. For example:
You can stack on top of a Proto Shield, but not if there is a breadboard on it
You can stack on top of an Adafruit Motor Shield v2
You can stack on top of a Wave, NFC/RFID, or GPS shield with no problems
You can stack on top of an Ethernet shield, but you'll need two sets of headers to clear the Ethernet jack.
You can't stack on top of our TFT or LCD shields
Some shields use the ICSP (2x3) header in which case you may need to solder in the stacking 2x3