In their simplest form, traditional stereo hi-fi systems or passives consist of a source component (which is the piece of kit that plays the music...can be a CD player, streamer, record player, digital audio player, computer, phone or even iPods? 🤭), an integrated amplifier and a pair of passive speakers.
But if you're a noble audiophile or your name is Shane and your source is mostly digital (Spotify, YouTube, Amazon Music, Apple Music, Tidal) it's worth getting a digital-to-analog converter (DAC). Next, add a preamp, this switches between sources and controls the volume level.
However, if your name is Pak Chong and you have a record player, you'll also need a phono stage to increase the output from your cartridge to line level and equalize the signal before feeding it to the preamp circuit.
Now you need muscle, something that can take the line level signal from the preamp and increase it enough to drive a pair of speakers - say hello to the power amplifier.