Navigation buttons- need some help

This is my first time creating a new WP theme.I have modified an existing WP theme with the content of a PSD that I created. I am still do not know everything there is to css, I am still learning it. I have entered my navigation buttons that I created in the CSS **menu structure area** and entered them in the header page. I am not sure where else I need to enter the information to display them.

Right now it is displays the one that the WP theme created(I have not removed it from the css) in the **begin MenuItem** which is .artmenu of the css that is displaying lower than where it needs to be. Should I have added mine in the **begin MenuItem** area of the css instead of the **menu structure** area? Also what php pages would need to be modified to have them display properly.

Thanks
https://jds-productions.com/wordpress/