Once you have received a link to a Private Sale, you will first be asked to open the proposal. This will allow you to see the full terms of the sale and a message from the seller, if they added one in.
Review all of the details to make sure they are in line with your agreement
Click "Accept Private Sale"
After you click to accept the proposal, you will be prompted to pay a gas fee from your wallet to complete the transaction
Once the transaction has cleared, the NFT will automatically be sent to your wallet and the payment will automatically be sent to the seller