Block explorers allow you to find transactions on the blockchain. They also index smart contracts and allow for direct interactions.
SnowTrace is Avalanche’s new "main" block explorer. It’s very similar to the likes of EtherScan (for Ethereum) and BSCScan (for Binance Smart Chain).
Avascan is another Avalanche blockchain explorer. Not affiliated with the minds behind Avalabs. They go a few steps further than SnowTrace does. Showing NFTs, and offering verification ticks to projects to tokens that deserve it.