First, you're on Desktop, install either the nos2x or Alby browser extensions. both of which will accept your nostr private key and intermediate login/signing requests from various web clients. This is safer than pasting your Nostr private key into various websites.
If you're on mobile, you can install Kiwi Browser from Aurora Store which allows for browser extensions on mobile devices.
The widget below is FiatJaf's nocomment, A Nostr-powered embeddable website comments widget that just works. Give it a try. Future posts will likely use this functionality.