Understanding Diacritical Marks in French

There are four French accents for vowels and one accent for a consonant. Understanding each of these accents is vital because they actually change the pronunciation of the letters that they modify, essentially creating completely different letters for the French language. 

Vowel Accents

The accent aigu ´ (acute accent) can only be on an E. At the beginning of a word, it often indicates that an S used to follow that vowel, e.g., étudiant (student).
The accent grave ` (grave accent) can be found on an A, E, or U. On the A and U, it usually serves to distinguish between words that would otherwise be homographs; e.g., ou (or) vs où (where).
The accent circonflexe ˆ (circumflex) can be on an A, E, I, O, or U. The circumflex usually indicates that an S used to follow that vowel, e.g., forêt (forest). It also serves to distinguish between homographs; e.g., du (contraction of de + le) vs dû (past participle of devoir).
The accent tréma ¨ (dieresis or umlaut) can be on an E, I, or U. It is used when two vowels are next to each other and both must be pronounced, e.g., naïve, Saül.

Consonant Accent

The cédille ¸ (cedilla) is found only on the letter C. It changes a hard C sound (like K) into a soft C sound (like S), e.g., garçon. The cedilla is never placed in front of E or I, because C always sounds like an S in front of these vowels.

Capital Letters

It is essential to put accents in their proper places; an incorrect or missing accent is a spelling mistake just as an incorrect or missing letter would be. The only exception to this is capital letters, which are often left unaccented.