You can verify your collection on Etherscan by selecting the blue Verify Contract link at the top of the management page.
When you deploy your smart contract, it will initially be unverified on Etherscan. This means that people viewing the smart contract on Etherscan won't be able to see the code. We highly recommend verifying your contract to provide transparency to your buyers.
Once the contract is verified, Etherscan will show a green checkmark, and people will be able to freely browse the smart contract code.