I cannot add menu items pointing to my other pages in the menu in my headers

I am new to wordpress. I am trying to add menu items to the menu in the headers, where the items point to my other pages on my site.
I have tried watching the wordpress teaching videos, and googled it. Something is always different than what i see or have.
How do i put a ‘link’ or menu item in my main menu in my header that points to or connects to another page on my site? How do i add a Cart option to my menus?

The page I need help with: [log in to see the link]