The word "fuss" is used when someone worries about a situation or causes a problem because of a very particular, personal preference.
In these examples, the word "fuss" is a verb:
Jeremy is always fussing around with puzzles.
Vanessa is fussing with her dress, trying to make it look right.
If you fuss with that recipe too much, you’re going to ruin it.
Stop fussing with that.
A customer who was fussing over the menu at Burger King made the people behind him wait until he finally made up his mind. (This is an example of a compound-complex sentence.)
The word "fuss" is also a noun:
It’s not necessary to make a big fuss out of this situation. (The verb "make" and the adjective "big" are often used with "fuss.")
The neighbors made a big fuss when Ronald parked his boat in the street.
If you make a big enough fuss about something, you’ll get the attention of other people.
Don’t make a fuss. Just be quiet.
The word "fussy" is an adjective.
Rachel is a fussy eater.
Walter is fussy about where he lives.
Some students are very fussy about where they sit in class.