From ChatGPT lol.

French uses three main accent marks (diacritics) on vowels:

Des Voyelles

1. Accent aigu → ´

• Found only on é
• It marks a closed "e" sound: /e/ (like in café or résumé).
• Often used to indicate the transformation of Latin words (e.g., étudier from Latin studiare).
• 📌 Examples

2. Accent grave → `

• Used on à, è, ù
• On è, it changes the pronunciation to an open "e" sound: /ɛ/ (like "bed" in English).
• On à and ù, it does not change pronunciation - simply helps to distinguish words:
  • à (to, at) vs. a (has, from "avoir")
  • où (where) vs. ou (or)
• 📌 Examples

3. Circonflexe → ˆ

• Used on â, ê, î, ô, û
• Often marks the disappearance of an old "s" in earlier French words.
  • forêt (forest) ← from Old French forest
  • hôpital (hospital) ← from Old French hospital
• It sometimes affects pronunciation, mainly with ê (makes it more open, like pêche /pɛʃ/ "peach").
• 📌 Examples

4. Tréma → ¨