Different ways to say "Thanks" or "Thank you"

Hi,

I do hope I don't annoy anyone by asking overly simplistic questions... but as I'm trying to learn just a little bit of Farsi as I'll be travelling to Iran next month. However, after having learned that "Thank you" is "Kleili Mamnoon" or "Mersi", the next video I watch it's said that it's translated as "Tashakkor Mikonam".

I was wondering whether they were just different ways to say the exact same thing, or whether they differ/are used in different ways or situations.

Kind regards