In the footer section, you can add a footer menu, which you can find in Shopify Admin > Online Store > Navigation.
You can add a menu item named "Contact Us" and link to the contact us page. This way doesn't require coding or third-party app.
I personally prefer creating a separate contact us page rather than including just the contact information. Because if you implement the page correctly, it can benefit your SEO and drive organic traffic.
You can take a look at this tutorial about how to build a contact us page. There's a video series, which is easy for beginner to follow.