Website is absolutely of no use if there is no navigation or menu in it. No one is going to scroll down one whole page without knowing which information is where. When designing a layout of the website ample time and space is given to the Menu and a lot of thought is put into how the menu bar would look like and what content is to be put in it.
Menus are of three types, Simple Menu, Drop down Menu and Mega Drop down menu and these menus could be created in a lot of different manners. They could be created in pure CSS or using the combination of HTML and CSS. You could have a look at some of the Best Mega drop down and Multi Level Menus Collection.
In the meanwhile you could also have a look at some really useful collection of CSS Button Generators for your inspiration!