What's all the fuss about

Fuss
function: noun
1 a : needless bustle or excitement : COMMOTION b : a show of flattering attention <made>
2 a : a state of agitation especially over a trivial matter b : OBJECTION, PROTEST c : an often petty controversy or quarrel <ended>

As you can see, the sentence is simply a way to say "What is all the commotion/excitement about?"
It is normally used in the company of friends, but is acceptable for use in all other parts of society as well. It has a definition as a verb, as shown below, but it changes nothing concerning the sentence.

Fuss
function: verb
1 a : to create or be in a state of restless activity; especially : to shower flattering attentions <fussing> b : to pay close or undue attention to small details <fussed>
2 a : to become upset : WORRY b : to express annoyance or pique : COMPLAIN
transitive senses : AGITATE, UPSET