OpenSea is the first decentralised NFT marketplace available, and was founded in 2018. The marketplace was not a household name until 2021 when NFTs exploded in popularity.
You can find plenty of NFTs in OpenSea, including digital items such as pictures, digital art pieces, domain names, music, trading cards.
To buy, sell or trade NFTs on OpenSea, you will need to have access to a cryptocurrency wallet such as MetaMask. The main currency on OpenSea is Etherum, but other currencies are also supported.
Buying and selling on OpenSea is highly secure. If you pay, you get the NFT.
OpenSea operates on the “Wyvern Protocol”, a series of smart contracts that ensure you get your cryptocurrency after selling your NFT and vice versa. It has been battle-tested and proven secure for these significant transactions.