This is the 9th most frequent Dutch word.
je
"Je" means "you" (informal, singular or general).
Here, 'je' is used as a possessive pronoun meaning 'your', indicating possession of the noun 'huis'.
Je huis is erg gezellig.
Your house is very cozy.
In this sentence, 'je' serves as a personal pronoun equivalent to 'you', acting as the subject of the verb 'valt'.
Let op dat je niet valt.
Be careful not to fall.
Here, 'je' is again a personal pronoun meaning 'you', used as the subject of the verbs in both clauses: 'kijkt' for the first and 'zie' for the second.