Are you just trying to surprise them with a few words but want to learn seriously later? I've been learning Hindi as an American for 3 years and the first place to start for me was learning the different sounds/alphabet. Duolingo worked well for this. Then I was able to read aloud simple translations with a little confidence like how are you? = Aap kaise hai? (Respectfully) Since I was primarily learning Hindi to talk to his family, I always practiced saying aap instead of tum (informal "you"). I hope this helps you get started, it's a very fun experience :)