Crypto can be confusing to people new to the field. There are the most prominent terms you need to know, ordered by priority (somewhat):

Generically for Blockchain

Blockchain: Decentralized network of servers/nodes that process transactions.

Blockchain transaction: The process of moving a token from one address to another address in a blockchain.

Address: The unique destination of tokens within a blockchain. Someone (like you) owns the private keys to that address and can therefor initiate transactions out of that address. Usually you can send tokens into any address, regardless of their permission (they may ignore it though). Think of it like a mailing address or email.
Cryptocurrency: A native token that can be send through the blockchain.

Token: A unit in a blockchain. This can be the native currency (e.g. Bitcoin, Ether, ADA etc.) but it can also be an NFT or another smart contract.

Smart contract: A specific token that is bound to rules. For example it can trigger automatic process when executed. NFTs are typically in the form of smart contracts.

Non-Fungible-Token (NFT): A token that cannot be split or reproduced. It exists only once in the blockchain but moves around just like other tokens.

Metadata: The “extra” information attached to an NFT, can be as simple as a picture URL (which is what you typically see) but can also be quite complex.

Rarity traits / traits: Characterics of an NFT within a collection that make it more or less rare than others.

Collection: The sum of all NFTs under the same banner. E.g. CryptoPunks or CryptoDads.

Opensea: The most popular and easiest to use marketplace for NFTs.

Minting: The process of creating an NFT. Usually there is a price for minting and a transaction fee (gas, see below).

Pre-Sale: Whitelisting of addresses that allow you to mint when transaction fees are low.

Generically for buying mainstream NFTs

Know this: There are many blockchains and many of them support NFTs. If you care about that it is super fun to learn about and you should definitely check it out. However, when we refer to “mainstream ” we consider what is used in most cases and that is: Ethereum NFTs on the Ethereum blockchain traded through Opensea, paid for with Ether (ETH). Let’s break it down:

Bitcoin: Most popular (and valuable) blockchain – also the first. Lacks features like NFTs and smart contracts though.

Ethereum: The second most popular blockchain after Bitcoin. In contract to Bitcoin Ethereum does support smart contracts and was the first blockchain to feature NFTs.

Ether: The native currency used on Ethereum.

Gas: The part of a transaction that is paid as a fee to the network in Ethereum. The more people want to process transactions the higher the gas fee will be.

Gas-Wars: When lots of people try to mint at the same time it can lead to extremely high gas-prices. To prevent gas wars NFTs often utilize pre-sales.

After reading all this you can go ahead and sign up for Metamask!