Email on your domain is two separate jobs. Sending is your site sending messages, like a contact form notice, from hello@yourdomain.com. Receiving is an inbox where you read mail people send to that address. You can do one, the other or both. They live side by side in your DNS without getting in each other's way.
Sending with Resend. Your contact form already works through Netlify Forms. You only need Resend if you want the site to send from your own address, or later for receipts and newsletters. Even then, verify your domain now: DNS takes time, and it makes your domain look trusted to inboxes.