The first part of your greeting in German is a basic hello. How you say hello depends on what time of day it is. The following list includes both the standard, formal expressions for saying hello and the more casual, informal expressions:
Guten Morgen! (gooh-ten mor-gen!) (Good morning!) This is the standard, formal greeting you use in the morning (until about noon).
Guten Tag! (gooh-ten tahk!) (Hello!) This is the most common formal greeting you use, except early in the morning and late in the day.
Guten Abend! (gooh-ten ah-bent!) (Good evening!) Obviously, this is the formal greeting of choice in the evening.
Hallo! (hâ-loh!) (Hello!) You should be pretty comfortable with this informal greeting because it’s very similar to English’s hello.
When the time comes to part, you can say:
Auf Wiedersehen! (ouf vee-der-zey-en!) (Goodbye!) This is the standard, formal goodbye.
Gute Nacht! (gooh-te nâHt!) (Good night!) You use this standard, formal farewell when you say goodbye late at night.
War nett, Sie kennenzulernen. (vahr nêt, zee kên-en-tsoo-lêrn-en.) (It was nice meeting you.) You use this formal phrase to tell people that you enjoyed meeting them for the first time.
Tschüs! (chues!) (Bye!) This is the informal way of saying goodbye.
People in Southern Germany, Austria, and German-speaking Switzerland certainly understand you when you wish them Guten Morgen/Guten Tag/Guten Abend (depending on the time of day). However, people in these regions also use some other greetings:
In Switzerland, you hear Grüezi (grue-e-tsee) (hello) most often, and people who know each other well use salut (sâ-lue) to say both hi and bye.
In Southern Germany and Austria, you say hello with Grüß Gott (grues got) or its informal version, Grüß dich (grues diH). Good friends express both hi and bye with the casual Servus (sêr-voohs).
Especially among younger German speakers, you hear the informal goodbye, Ciao (chou), or the German-spelled version Tschau (chou), which has made its way north across the Alps from Italy.