If you want a button the when clicked will open the reader's email program with your email address already filled out, create a navigation button and double click it to open the properties. Then select the button and Edit. Change the name to Contacr Us (or similar) and for Link Type change to mailto and enter your email address in the space below.
However, a Contact form is recommended and is easy to create if you watch the tutorials.
HERE
beginning with #20.
The form will help prevent spammers from harvesting your email address.