An implementation of contact info form is already shipped with Plone, just go to the /contact-info page.
If you need something more, please be more specific.
About dropdown menu: there are lot of add-ons for this (not sure if anyone is Plone 5 ready) but IMHO those kind of add-ons are less critical nowadays as Plone 5 use Diazo all the way around; so you can simply add a dropdown menu found of the web directly on your theme.
Once again: it depends on what you need to obtain... a static menu is simple, a dynamic ones requires some work.
See also this discussion: Plone 5: Dropdown menus