Price: The price details how much it costs to purchase the NFT(s), the price can be in either Ada or any other Token the owner wishes to charge for an NFT, potentially allowing a buyer to pay with either (examples below). The price represented here is the final price, meaning if you increase the quantity of NFT's you are purchasing, the price will reflect that. i.e purchasing 2 NFT's that cost 4 Ada each will show the price as 8 Ada.
Quantity: This is the amount of NFT's you are purchasing when you press the "Mint NFT!" button. Project owners often set a maximum number on this. (i.e. you can only choose to purchase 10 at once).
Mint NFT button: Pressing this will allow you to purchase the amount of NFT's displayed in the Quantity, when pressed a popup will appear asking you to sign a transaction, this act signs the transaction and sends the buy order through the blockchain.
When the Mint button is grey, it means that a person cannot mint anymore NFT's, either because there are no more NFT's, or because a transaction to mint is going through.
Show Collection Data button: This button displays the individual stats of the Mint, particularly how many NFT's have been reserved (someone is currently in the process of purchasing them) and how many NFT's have been minted (bought).