Commas are used to separate a string of words - unless those words are joined by conjunctions such as "und" and "oder". Usually the last word listed is preceded by "und". In that case, there is no comma in front of it.

Examples:
Nein, nein, nein!
Nein, nein und nochmals nein!
Ich brauche Stift, Papier und Informationen von dir.

The same applies to groups of words, clauses and to join two independent clauses of equal ranking.

Grammatical phrases:

Example:
Wo war der Mörder - vor der Bank, in der Bank oder im Hinterhof?

Dependent clauses:

Example:
Ich möchte auch wissen, wer das getan hat, wer mein Mörder ist.

Independent clauses:

Examples:
Ostrowski wird uns nicht helfen, Anderson wird uns nichts sagen.
Ostrowski wird uns nicht helfen und Anderson wird uns nichts sagen.

Two independent clauses joined by the conjunction "und" do not require a comma. But a comma can be used nonetheless to make the sequence of events in the sentence even more clear, especially if the two independent clauses have different subjects.

Example:
Ich erinnere mich an den Hinterhof, und dann war da der Schuss.

More:

In German, the following coordinating, subordinating and correlative conjunctions join together words, groups of words or clauses of equal ranking, so they are usually not preceded by a comma: "und", "oder", "bzw."/"beziehungsweise", "sowie", "wie", "entweder ... oder", "sowohl ... als auch", "weder ... noch".

A comma precedes the conjunctions "denn", "aber", "jedoch", "doch", and "sondern".