How do I know what amplifier I need?

I'm curious, how do I determine which amplifier is the best fit for my needs? Is it based on the type of audio equipment I have, the size of the room, or both? And what about the power output, does it play a significant role in the overall sound quality? Additionally, are there any specific features I should look out for when making my selection? I'm hoping to get a clear understanding of the factors that influence the choice of an amplifier so I can make an informed decision.