Heh heh when I said “un-opinionated” I meant that in the fullest sense.
There isn’t a menu builder- there is a nav component that most designers utilize and it’s usually at the top of the page, typically inside of a component ( these generally show as green in the nav ).
You’re approaching this cliff from the hardest possible angle- try simple things first. Webflow U has a ton of videos and courses on each of the parts you need to learn.
For someone new to WF, start at the beginning with the 101 even if you have years of web design, it will save you a ton of time. Then go to the courses specific to navs and components.