It is punctuation convention, a kind of markdown that helps you see what the structure is. Independent clauses are set off by commas; conjunctions like а, но usially have commas before them even if they only contrast words, not clauses.
Lists are punctuated pretty much the same as in English but without an Oxford comma. "Both ... and ..." structure и ... , и ... has a comma before the second «и» and all и's that follow, unless the whole phrase is a set expression. This goes for «ни ..., ни ...» and «или ..., или ...», too.
Commas and dashes do not, as a rule, correspond to any pauses in speech. Intonation, maybe? After all, the structure of a sentence affects intonation.
We accept both here but they are not the same (just the meaning overlaps in this case). «Узнать» is "to find out, to learn". Essentially, it is the difference between "to sleep" and "to fall asleep". «Знать» describes a state and, as such, does not even have a true perfective form.