Contract Chain (C-Chain)
The C stands for contract, and this is the chain that’s used for smart contracts and
Defi apps. The key difference with the other chains is that the c-chain uses an Ethereum-style address with 0x at the beginning, which can be added to your MetaMask.
Most Avalanche Defi platforms such as AAVE, Trader Joe, and Benqi work on the C-chain and are compatible with Metamask.
Exchange Chain (X-Chain)
The X-chain is used for sending and receiving funds, however, it is not used for Defi platforms. Also, note that x-chain cannot be used with MetaMask or similar wallets. Your X-chain address is accessed from the Avalanche web wallet, and you get a new address after every deposit (note that your old addresses remain valid too). The format is different from Ethereum-style 0x addresses and begins with a "X-avax".
Platform Chain (P-Chain)
The final chain that Avalanche offers is the p-chain (for the platform). The P-chain's function allows you to stake AVAX and serve as a validator. If you are a validator or delegating to a validator, then your AVAX rewards will be received on this chain. Note that these also differ from Ethereum-style 0x addresses and begin with a "P-avax".