Why is it asking me for credit card details?
I have already paid for the product.
It is asking for credit card details since you have selected the option "Auto-renewal" by clicking "Agree & Continue".
If you want to opt out of auto-renewal, just click on the blue "X" on the top right side of the popup window.
Then click on "Continue".
Click on Install on this PC.
Click on I agree.
Click on Download button to download the McAfee Setup file.
Run the downloaded McAfee Setup file to install McAfee.