The German v has actually two different sounds. One is like the English (and also German f). That means that there are actually two letters having the same sound (=f).

Vogel bird   vornehm   noble   Vorsicht   care

But then it can also have The sound like the English v (or in German a w). So the German w-sound and the German f-sound have two possibilities to be expressed. With w=v, and with f=v.

die Villa villa Vase vase Klavier piano Jagdrevier hunting area

Once more for your comparison:

Vetter cousin Vollmond full moon Veilchen violet Volk people (e.g. Indian people)

Darüber wundert sich das "V" Obwohl ich immer als "V" vor dir steh', bin ich manchmal ein "F" und manchmal ein "W". Im Klavier und im Jagdrevier Wird ein "W" aus mir. Du siehst mich als "V", doch wie sagst du dann? Willa, Wase und Pawian. Nur aus dem Vollmond, das wäre zum Lachen, dürftest du keinen Wollmond machen, und aus dem Veilchen kein Weilchen, aus dem Vetter kein Wetter. Ich bin manchmal ein "F" und manchmal ein "W", obwohl ich immer als "V" vor dir steh! What the "V" is wondering about Although I stand as a "V" in front of you, I am sometimes an "F" and sometimes a "V". In Klavier and Jagdrevier I turn into a "W" You see me as a "V", but you say Willa, Wase and Pawian ? But the Vollmond, that would be funny, you don't make into a Wollmond. and from Veilchen you don't make a Weilchen. and from Vetter you don't make a Wetter. I'm sometimes an "F" and sometimes an "W" even though I always appear as an "V".

The poem plays with words which are hard to translate. We'll try anyway:
Vollmond = full moon
Wollmond = woollen moon

Veilchen = violet
Weilchen = little while

Vetter = cousin
Wetter = weather

So in these cases it's better to be a bit careful because used the wrong way it can cause something between funny evenings and bigger misunderstanding.