Dear driver in front of me that's constantly tapping your brakes to adjust your speed... you do not need to do that.
Simple let off your throttle pedal and let the engine do some of the work for you. You'll save some of the useful life of your brake pads, see better fuel economy, and (most importantly) not agitate your fellow motorists.
Your engine works as a delightful tool to not just speed your car up but also slow it down. When you lift off the throttle in a gasoline-drinking car, you're closing the throttle body. This lets air into your engine during the intake stroke of the combustion process. When the throttle body is closed, the air can't get in when your engine is completing its combustion process so it's now slowing you down and acting as a brake.
A similar event happens in diesel vehicles as well. Instead of creating a vacuum from the closed throttle body, however, the diesel engine utilizes backpressure as its means of engine braking. There's an additional method of engine braking in a diesel and it involves the use of a Jake Brake. We'll let Engineering Explained talk you through that one in the above video.
Also, if you're experiencing engine breaking then you need a different video, some tools, and probably a visit to your mechanic.