Formal:
* Gràcies: This is the most common and polite way to say thank you. It's suitable for most situations, even when addressing someone you don't know well.
* Moltes gràcies: This means "many thanks" and is even more formal and polite than "gràcies".
Informal:
* Merci: This is a shorter and more casual way to say thank you. It's more common among friends and family.
* Gràcies, eh?: This is a very informal way to say thank you and is often used among close friends.
Other ways to express gratitude:
* Estic molt agraït/agraïda: This means "I am very grateful" and is a more emphatic way to express your thanks.
* T'ho agraeixo molt: This means "I thank you very much" and is a more personal way to express your thanks.
Example:
* Gràcies per la teva ajuda. (Thank you for your help.)
* Moltes gràcies per venir a la meva festa. (Many thanks for coming to my party.)
* Merci per el regal. (Thanks for the gift.)
* Estic molt agraïda pel teu suport. (I am very grateful for your support.)
Remember that Catalan is a language with a rich history and culture, and the best way to express your gratitude is to use the language that is most appropriate for the situation.