For example this: Difference between a sentence and a proposition in philosophy
For me that's a perfectly good and interesting question and a typical puzzle for beginners in philosophy. And it also has an answer:
There are basically two different uses of the word "sentence" in philosophy: sentence as a syntactic object (in type or token sense), and sentence as a meaningful sentence.
The latter use partially overlaps with the notion of a proposition, this can be elaborated, and it can be confusing.
"Proposition" is similarly ambiguous.
The modern technical use of things like propositions was to my knowledge pioneered by Bolzano, but it would be easier to start from Frege. Frege was the first to propose a compositional theory explaining how the structure of a sentence represents the structure of a proposition. Russell is the other historically important figure here. (The contrast between Russellian vs Fregean propositions should be hinted at.) From Frege you get the modern version of propositions as structured objects. In the 1970s (?) the idea of propositions as sets of possible worlds was also popular (this is a version of the unstructured propositions approach).
Here you could also say a couple of words about why philosophers think they need propositions, and what is the metaphysics of propositions.
That's only a sketch and I don't have time to flesh it out at the moment, but the point is that the question has in my view a standard answer. So why close it?