Resetting the Non-Volatile memory and System Management Controller is one way to troubleshoot problems with your Mac. But the methods for resetting those have changed with the latest hardware which include T2 chips. Most users will never have to deal with these, but if you do, learn Apple's recommended method for resetting these.
If you've ever had trouble with your Mac in the past you may have been told that to fix it you need to reset the NVRAM or reset the SMC. Now things have changed a bit. With the newest Macs coming out in 2018 and forward there's a T2 security chip and it changes a little bit about how a Mac starts up. So you have to change how you reset these. I want to mention that for most Mac users you can go your entire life and never have to deal with resetting the NVRAM or the SMC. But if you do this is how you would do it and especially if you're getting a new Mac this is how you're going do it going forward.
So note that the NVRAM that stores settings, you know, hardware settings like display resolution, volume, which disk is being started up.Things like that. So that's what's stored there. If there's any issues you think are related to those then you may need to use this. Usually it's something where you run into an issue and you're searching online for a solution and you read somewhere that Oh! to fix that reset the NVRAM.
Doing it on Macs, old and new, is a matter of holding the Option, Command, P, and R keys and starting up the Mac. So it's shut down. You hold these keys to start it up. Now on the newer Macs the only difference is that you release the keys after the Apple logo appears for a second time. Whereas previously you can release the keys after the second startup sound. So it's a little bit different but basically it's the same thing.
Now resetting SMC is a little different. SMC does a bunch of different things also a lot to do with hardware. It's basically low level system stuff. So it's stuff that handles, on your Mac, you know outside of the operating system. Like battery management. Pressing the power button. Your Mac is off so how does it recognize pressing the power button. Thinks like that. Apple has a list here at this page of a whole bunch of things that could be issues that you need to reset the SMC. They also include some information here like what things you can do before hand.
Now there's a bunch of different instructions on this page. Basically on Macs you hold the Shift, Control and Option keys on the left side of the keyboard and the power button to do it. A little bit different on desktops. You basically unplug the power cord. There's no battery to keep power going to the machine so basically unplugging the power for 15 seconds will work.
Now if you've got the T2 chip then you've got a few things to do first. So if it's a desktop you hold the power button for 10 seconds after your Mac shuts down. Then it also recommends unplugging. Now if you have a Notebook computer so there's a battery in it you can do the same thing. So it's nice that you can kind of go and do the same thing on desktops and notebooks now. It has some instructions that if that doesn't work what to do.
Now what are these T2 security chip computers. Well, these are the new Macs that came out. So if you have an iMac Pro it's got one. Any Mini or MacBook Pro or Air models in 2018. So the machine was introduced in 2018. Not necessarily when you bought in 2018. You could have bought an older 2017 model in 2018 for instance. You can go to System information and you can look at the Controller and it will say model name Apple T2 Chip under Controller. So that's how to determine whether or not you've got a Mac with a T2 Security Chip and you could just use these pages to figure out what you need to do should you ever need to reset the NVRAM or SMC.
Links: Reset NVRAM or PRAM on your Mac, How to reset the System Management Controller (SMC) on your Mac, About the Apple T2 Security Chip.