This is the 111th most frequent Polish word.
tu
"Tu" in Polish means "here."
In this sentence, 'tu' is used as an adverb indicating 'here', specifying the location of the house.
Tu jest mój dom.
Here is my house.
Here, 'tu' is again an adverb meaning 'here', describing the place where the speaker is.
Nie mógłbym być tu bez twojej pomocy.
I couldn't be here without your help.
In this sentence, 'tu' specifies the location where the observed things are located.