Smart contracts on the explorer
A smart contract is a small program that lives on the chain at its own address. Instead of a person holding the address, a piece of code does, and that code runs exactly as written whenever someone sends it a transaction. Tokens are contracts. So is anything that calls itself an app on a blockchain.
When you open an address that turns out to be a contract, the page says Contract and gains an extra tab.
Verified and unverified
A contract on the chain is stored as machine code, which nobody can read. Verification is the step where the author publishes the original human-readable source and the explorer checks that it really does compile into exactly the code sitting on the chain.
A green Verified mark means that check passed. It tells you the code you are reading is genuinely the code that runs.
It does not tell you the contract is safe, fair or honest. A well-written scam verifies just as cleanly as anything else. Verification answers "can I see what this does", not "is this a good idea".
An unverified contract is not automatically bad, but it is unreadable, and nobody outside its author can tell you what it does.
Contracts in the Blockchain menu lists every verified contract on the chain.
Inside the Contract tab
Code shows the published source, along with which compiler produced it and whether the match was exact or partial. A partial match means everything matches except a technical fingerprint at the end, which is normal and not a concern.
Read contract lists the questions you can ask it. These are free, they change nothing, and they need no wallet. Asking a token contract for its total supply is a read.
Write contract lists the actions that change something. These are real transactions: they cost a fee, they need a wallet, and they cannot be undone.
If the contract is a proxy, a notice says so. That means the address you are looking at forwards everything to a second contract that holds the actual logic, and the read and write tabs use that second one.
About the write tab
This is the only place on the explorer where a wallet gets involved, and it is the only place where you can lose money by clicking.
Calling a write function does exactly what a wallet or an app would do, except that nothing dresses it up or explains it. There is no confirmation screen describing the consequences in plain language, because the explorer does not know what the function means. If you are not certain what a function does, do not call it here.
This part of the explorer exists for developers and for people who deliberately want to talk to a contract directly. Everyone else can use everything else on the site without ever connecting a wallet.
If someone tells you to use this page
Treat it as an alarm. "Go to the explorer, open the write tab and call this function" is a standard way of talking people into approving something they do not understand. Nobody legitimate needs you to do that, and no support desk will ever ask it of you.