This is the 119th most frequent Portuguese word.
minha
"Minha" means "my" (feminine singular).
In this sentence, 'minha' is used to indicate ownership of the 'pen' ('caneta'), specifying that it belongs to the speaker.
Onde você deixou minha caneta?
Where did you leave my pen?
The word 'minha' is a singular, feminine possessive adjective meaning 'my', referring to something owned or related to the speaker, here in the context of 'house' which is 'casa' in Portuguese.
Minha casa está no centro da cidade.
My house is in the city center.
Here, 'minha' again indicates possession, showing that the 'water bottle' ('garrafa de água') belongs to the speaker.