Guten Tag, Servus, Grüezi and more ...

People greet each other with lots of different expressions, depending on whether they are from (or at present in) Northern Germany or Southern Germany, Austria or Switzerland. Guten Tag is the normal standard German expression, replaced in Austria, Switzerland and Southern Germany by Grüß Gott. A typically Austrian greeting is Servus, but Grüß Gott is being used there more and more. In Switzerland Grüezi or Grüezi mittenand are still the main standard greetings.
If you want to be less formal, there is a wide variety of expressions to choose from. You can opt for Hallo, or in the south Grüß dich. In Switzerland you can say Salü, which of course is French. English Hi is getting more and more popular among teenagers and young people.
When you say goodbye, simply say Auf Wiedersehen, or alternatively Servus in Austria. In Switzerland you can opt for Uf Widerluege, if you find you can pronounce it easily enough. In fact it's not that easy for native speakers of German from other regions either.
Less formal and very common is Tschüs. People also say Ciao, from Italian, or in Bavaria Pfüati, a real tongue-twister. In Switzerland people prefer French Adieu best of all. Whether you say Adieu, Tschüs or Ciao depends on where you are and what your personal preference is.
It's probably better not to use Austrian Baba. That's very familiar and only really sounds convincing when spoken by an Austrian.