Hola, Mohamed!
The name of the symbol on top of the vowels ( ´ ) is called in Spanish: 'tilde'. It's an ortographic and very important symbol that needs to be written to understand full ideas or express different meanings.
Sometimes, you need to write to say different grammar categories, for example:
- él (he) personal pronoun
- el (the) article
But the pronunciation is the same.
The difference between 'que' y 'qué':
"Qué" (with 'tilde') is used for questions and exclamations: "¿Qué es eso?" / ¡Qué chica tan guapa! In these cases, we can put more emphasis on the pronunciation.
"Que" (without 'tilde') is a relative pronoun, that means we introduce a special description for the nouns in a sentence, is like English "that". For example: "Me gustan los gatos QUE tienen pelo negro" (I like the cats THAT have black hair).