Really confused about how to reset SMC and PRAM and NVRAM on my Macs and iPad and iPhone?
Sorry to hear you’re having problems. I hope the following clarifies things for you, but if these instructions do not help, you can always post specific questions about any problems you’re having.

SMC

The reason for your confusion is that the instructions for resetting the System Management Controller (SMC) will differ depending on whether your device:


runs from a built-in battery?
runs from a removable battery? 
can only run from power off a wall socket?


Below I will provide the instructions for all three possibilities.

For MacBook Pros, MacBook Airs, and MacBooks where you can’t remove the battery on your own (i.e. it's a built-in battery), here’s what you do:


Shut down your computer
Keep the MagSafe adapter (or power cable) plugged in.
Press at the same time shiftoptioncontrol (on the left side of the keyboard) and the power button
Let go
Turn your computer back on with the power button.


For MacBook Pros, MacBooks etc that you can remove the battery from, here’s what you do:


Shut down your computer
Disconnect the MagSafe plug (power cable) from the computer
Remove the battery
Press the power button for 5 seconds and release
Put the battery back in
Reconnect the MagSafe cord (or power cable)
Turn your computer back on with the power button


For iMacs, Mac Pros, Mac Minis, etc that only run from a power point in the wall


Shut down your computer
Unplug it from power
Press and hold the power button for 5 seconds
Plug it back in and turn it on.


PRAM/NVRAM

Now, the reason for your confusion about PRAM and NVRAM is that older Macs had what's called Parameter RAM (PRAM), newer Macs use Non-Volatile Random-Access Memory (NVRAM). 

Until recently, the instructions for resetting this were the same regardless of your Mac model. However, the Late-2016 MacBook Pro models use a different process. Below are the steps for both scenarios.

Resetting the PRAM/NVRAM on all models EXCEPT for Late-2016 MacBook Pro models


Shut down your machine. Yes, a full shut down, not just logging out.
Press the power button and then press the commandoptionpr keys. You have to make sure you press these keys before the gray screen appears or it won’t work.
Hold those keys down until your Mac reboots again and you here the startup chime.
Let go of the keys and let your Mac reboot normally.


Note: When you log back in you may need to readjust some of your system preferences (e.g. speaker volume, screen resolution, startup disk selection, time zone information, etc).

Resetting the NVRAM on Late-2016 MacBook Pro models

For all Late-2016 MacBook Pro models (with and without Touch Bar) follow these steps:


Shut down your machine. Yes, a full shut down, not just logging out.
Press the power button and then immediately press the commandoptionpr keys. 
Keep these keys pressed down for at least 20 seconds!
Let go of the keys and let your Mac reboot normally.


Note: When you log back in you may need to readjust some of your system preferences (e.g. speaker volume, screen resolution, startup disk selection, time zone information, etc).

iPods, iPhones, iPads

Devices running iOS do not have an SMC or PRAM/NVRAM that you can reset like you do on Apple Macs.

However, most random issues can be resolved by rebooting your device. To do this, hold down the Power button and Home button simultaneously for about 10 seconds until you see the Apple logo appear. After your device reboots you may need to enter your passcode.

In more serious cases, you can also access a range of reset options from Settings > General > Reset. Be careful though when deciding if/which option to select.