How do I add a contact form?

There are many free and paid plugins you can activate to do this quickly and easily. Contact Form 7, Ninja Forms, and Caldera Form are very popular but there are many more. Just go to the WP Dashboard Plugin > Add New > Search for Contact Forms > Install > Activate > Go to Plugin UI > Follow Plugin Directions. I used to use custom written HTML form with a php script back in the day which can still work for WordPress site if you want to go ol skool.