What are Avalanches 3 main Blockchains?

Excuse me, I'm a bit confused about Avalanches and its Blockchains. Could you possibly explain to me what are Avalanches' three main Blockchains? I've heard they play a crucial role in the cryptocurrency ecosystem, but I'm not entirely sure how they work or what their specific functions are. It would be greatly appreciated if you could break it down for me in a simple and understandable manner. Thank you in advance for your assistance.