as far as I know OpenSea uses Project Wyvern Exchange for bidding, offering, buying and selling. But I can't understand how it is works. Does anyone knows what is it? If anybody can explain it in very basic level (I don't need to so much detailed), I'll be appreciate!
Their documentation is at their website https://wyvernprotocol.com/.
In order to understand the fundamentals of Wyvern Protocol you'll need a deep understanding of blockchain and smart contracts. If you have smart contract development experience then you'll gain the best understanding by looking at their tests in their github repo.
The basics of the protocol are straightforward, two users agree to a trade. The trade is comprised of User A offering digital assets and User B offering digital assets.
Both Users agree to the exact same conditions for the trade and the wyvern protocol makes it happen.
An example would be: User A has two ERC1155 tokens they want to trade to User B for 1.5 wEth. User B has 1.5 wEth they want to trade for two ERC1155 tokens.
The trade itself agreement is all digitally managed on the blockchain using abi