This is the 6343rd most frequent Portuguese word.
dau
"Dau" is not a standard Portuguese word. It may be a typo or abbreviation.
In this sentence, 'dou' is used in the conditional sense suggesting intent to give a book in the future.
Se você quiser, eu dou o livro amanhã.
If you want, I will give the book tomorrow.
Here, 'dou' is the first-person present singular conjugation of the verb 'dar', meaning to give.
Eu dou o meu melhor em tudo que faço.
I give my best in everything I do.
Again, 'dou' is the first-person present singular conjugation of 'dar', used in the context of teaching or imparting knowledge.