In ERC721 and ERC20, we write our smart contract, but in solana, we are only using cli or the javascript to deploy the existing written program (smart contract).
Can we write our own program in solana, if yes how and does this support the platforms like opensea ?
Yes Solana allows you to write your own smart contracts, you are not restricted to using only existing smart contracts.. Let me help with some resources that will guide you on your learning phase.
To really get started on smart contracts use the solana cookbook https://solanacookbook.com/
Solana is a blockchain like Ethereum or Polygon but stands out for it super fast and low fee nature. Meaning you can also write smart contracts on Solana as it is done in other Blockchain but this time with the help of Rust or C programming language. Get started here.
OpenSea is a marketplace so it's the one supporting Solana and the contrary. Yes OpenSea supports Solana blockchain.
