Some words can to be more easy for who know, but for someone, principally for the people that don't know and/or don't speak English very well these words are of extreme important.
We can say that theses words are the "key words".
Let's see some example:
Thank you! (Obrigado!)
Hello and hi. (Olá e oi.)
Excuse me. (Com licença!)
Please! (Por favor!)
You're welcome. ( de nada.)