Power amplifiers snag low-level audio signals from preamps and “amplify” them (thus, the name, obviously) to a level that can drive speakers. Some amps are “integrated.” Integrated amplifiers have preamps built into them, so there’s no need for an external preamp. Some audiophiles look down on integrated amplifiers, while others are more lenient in their views... Nonetheless, some people prefer “power amps,” which if you haven’t guessed by now, do NOT have preamps built into them and require an external preamp.
This blog post discusses the makings of a power amp, with various comments and suggestions for preamps and power amps.