Blockchains are a secret way of transacting money and hiding the exchange of funds from others and authorities.
A blockchain is a transparent ledge, meaning that anyone can explore the transactions on it when given the tools. Those tools exist for all blockchains (except the few privacy chains that have been created that do in fact hid the exchange of funds).
Explorers allow anyone to search and explore all the transactions on the blockchain. The blockchain can be searched and explored in numerous ways using: wallet addresses, transaction IDs (TX ID), block numbers, epoch number, slot/epoch number, stake pool ticker, token ticker, staking keys. Users can also search for individual assets and transaction metadata if they have the information. Developers can use APIs to scrape data from the blockchain to inform all sorts of processes, programs, and to create data sets.