Solana Explorer is a blockchain explorer that allows you to view addresses, activities, and blocks of the Solana network. Block explorers are crucial tools for people who want to follow transactions and what is going on in the world. 

When deploying a smart contract you will be provided a link to Solana Explorer that is to the address of your smart contract. It is good to get comfortable using Solana Explorer as a developer as it can give you some important information and insights about the Solana blockchain.

There are some other explorer options on Solana like Solscan and SolanaFm. These explorers are available for testnets also.