In most small audio project hobbyist are using specialized audio amplifier chips. That’s really fine you get high quality amplification without scratching your head. Some probably don’t care how these things work. But don’t forget that amplifiers can be built out of discrete electronics components like bipolar transistors. Check out this great hackaweek project where Dino builds class AB audio amplifier out of three bipolar transistors and other passive components.
He slightly goes through theory of operation and of course demonstrates its working in following video.
Just to be quick… Class AB amplifier consists of two amplification transistors NPN and PNP where on transistor amplifiers positive side of signal while another negative. This way we get push-pull effect. So don’t afraid building discrete circuits – they are fun and you learn a lot. And who knows may be your next project will have amplifier out of discrete components.