When you're on an item page, click the Buy now button and follow the prompts in your wallet. Once the transaction is complete, the item will transfer to your wallet and the seller will receive the funds.
If another user is attempting to purchase the same item, you’ll see a notification in the purchase flow.
This is to let you know that it’s possible your transaction may fail. You can read more about failed transactions in this help guide.
Once your transaction is completed, you can return to your profile and click the Collected tab to see your NFT.
Keep in mind, there might be a slight delay before it's visible due to transaction processing time.