Almost every camera in existence (at least every one I've ever used) comes out of the box with the autofocus activation linked to the shutter button. While this is generally fine for a lot of situations, there's a better method out there, and this great video will show you why and how you should use it.
Coming to you from Tony & Chelsea Northrup, this helpful video talks about back-button autofocus. Simply put, back-button autofocus means you program your camera so pressing the shutter no longer activates the autofocus system, instead moving that function to a button on the back of the camera, typically so your index finger still depresses the shutter and your thumb activates the autofocus. This makes your life easier and improves shooting in a lot of conditions. Furthermore, as they mention in the video, some cameras let you customize them to the degree that you can program different focus modes into different buttons. For example, I have my Sony a7R III set up identically to them, using the AF-ON button for normal autofocus and the AEL button (whose standard function I never use anyway) for Eye AF. This is great, for example, if I'm shooting an event and want to grab a quick portrait of someone. Check out the video above for the full breakdown.