Dziękuję

1. polite
2. neutral
3. used with strangers, adults, formal situations

Meaning: “Thank you.”

Examples:

1. At the store
2. To your teacher
3. To someone older
4. In polite conversation

Very safe and always correct.

Dzięki

1. informal
2. friendly / casual
3. used with friends, family, people your age

Meaning: “Thanks!”

Examples:

1. To a friend
2. To your husband
3. In texts
4. Casual moments