can any plz tell me how to do it

i need some more help..i am just new in this development industry thats y not familiar with most of the things…

i am a great fan of the https://www.thechive.com site and i want to make a the drop down list of categories in the top navigation bar but dont know how to do that..can you guide me plz
and one more thing…in this website only one picture shows at the main post rest of them appear when u open the post…
but in my case when i try to put pictures in my post they appear in thumbnails ..all of them showing up in a single post
can any one tell me that how to do that