Why are there so many hyphens and apostrophes in French? What do they mean?

In French indicate (as in most other languages) the disappearance of a letter (it's = it is) , on the other hand, often have a euphonic raison d'être (which is typically French).

I do not think that there are more apostrophes in French then there are in English. At least I never noticed. English has the Saxon genitive that is materialised by an apostrophe.

Hyphens are a different story. French treats differently than English its compound words. Where in English one would acceptably write "blueprint" or "weekend"; where in English people tend more and more to write thank you (or even thankyou) instead of thank-you, French remained faithful to the double origin of the compound words. No one in France would dream of writing grandfather; the term is and remains grand-père.

The reason may be the simplifications contributed by Anglo-American usage (but this is not only often incorrect, but historically doubtful).

It must be noted however that some Americans do write "nite" and "lite" which no francophone Canadian would dare doing to French.

Furthermore, Francophones have a real cult of their language worldwide. France has a language Accademy whose linguistic decisions are published by the Journal Officiel and discussed by the Evening News. They also care the way their language sounds. To give one (out of many) example, they have a special use for the consonant "t" that I have never encountered elsewhere.

Suppose you had to say "que reste il" (ke reste il). The nearness of the two vowels (e and i) it is not only difficult to pronounce, but is ugly. To solve the problem French introduces an entirely arbitrary, double hypheneted "t" (euphonic) between them whose function is solely to make the phrase sound better (que reste-t-il). Isn't (is not) this wonderful? Languages, with their ways and means are incredible.

Never fall in the trap: "why should I learn a second language since everyone speaks mine". It is a totally idiotic posture. The more languages you speak, the better you understand the world, and the better person you are.