To add on here, Alchemy is a developer platform. That means it provides a suite of developer toolings and abstractions including JSON RPC APIs across all major chains, an ethers.js SDK, and a library of enhanced APIs like their NFT APIs. OpenSea, Aave, and The Graph all use Alchemy as their blockchain infrastructure provider. Alchemy doesn't just provide an API key that serves as a RPC endpoint to connect to various blockchains, but also has lots of tooling to read and write easier to blockchains.
When deploying smart contracts, Alchemy can be used in conjunction with things like Metamask, Solidity, HardHat, and ethers.js. Or Remix. An example of this is in Alchemy's beginner smart contract tutorial.
Remix is an online all-integrated IDE that lets you test, deploy and execute smart contracts from the comfort of your browser tab. If you decide to use Remix, Alchemy can help as the RPC endpoint to accurately and reliably communicate with the your selededed blockchain.