Explain and illustrate the difference between a sentence and a proposition in philosophy
There's some disagreement among professional philosophers about the relationship of the terms "sentences" and "propositions."
I would say the most important distinction is captured pretty well in the other answer but that it might be considered misleading to say that "a proposition is a form of a sentence."
The key distinction is that sentences are the things people say and that occur in normal languages whereas propositions are things that are either true or false.
On first glance, this seems like an unnecessary distinction. But there's several reasons it does prove helpful.
Snow is white.
Schnee ist weiss
All express the same propositional content but they are different sentences (there can also be difference sentences for the same proposition in the English). The same content can also be expressed symbolically in any of several logics.
For this reason, many philosophers would not want to call a proposition a sentence. This point is confusing because a proposition will/can be written as a sentence. But the expression would not be considered identical with the propositional content (the thing that can be true or false).
You can find some further explanation here.