To create a Contact page go to Shopify Admin > Online Store > Pages and click on 'Add page' button. In the bottom right corner of page editor specify 'page.contact' template in a 'Template suffix' option.
To customize the appearance of the page open Theme Editor (Shopify Admin > Themes > Customise), select 'Contact Us' from the dropdown located in the top area, then click on 'Contact Page' section.
Here you can customize the overall appearance of the page and add the following content blocks (content blocks are a similar thing to Homepage sections):
- Page Content
- Contact Form
- Google Map