For learning purposes, the obvious and most mainstream choice to start is Ethereum. Even if your intention is to create a cryptocurrency on other blockchains, you'd still want to start on Ethereum. Why? Because most other smart contract platforms are accommodating toward Ethereum developers, and many of them are compatible with EVM (Ethereum Virtual Machine).
Once you are able to deploy your own cryptocurrency token on Ethereum, you will be able to create tokens on Polygon, Binance Smart Chain (BSC), Avalanche, Optimism, Fantom, and many others. The processes are mostly the same.
By the way, Ethereum crypto tokens are almost always issued as ERC-20, which is the implemented standard for fungible tokens on the Ethereum blockchain. On alternative chains, they usually (although not always) follow the same numerical term, such as the BEP-20 token standard on Binance Smart Chain.
So, where to start? Well, there are multiple ways to start creating ERC-20 tokens. You can use tools like cointool.app
where you don't need to know how to code. But since this is a guide on how to create a cryptocurrency on your own, we will need a bit of knowledge of Solidity, the programming language used to build smart contracts in Ethereum Virtual Machine.
But don't worry, even if you have zero knowledge of Solidity, you can just copy-paste the codes you are going to see below, and you will still be able to create a crypto token. However, it's important for you to have basic knowledge of Ethereum blockchain, Etherscan, and Metamask. Also, check out our Metamask guide article