Some examples to clarify:

German 'f', German 'v' and English 'f' = /f/
Freitag, für, davon, vergessen
Friday, funny, office, stuff

German 'w' and English 'v' = /v/
warum, Mittwoch, Auswahl
very, over, love

English 'w' = /w/
(no German letter equivalent)
when, away, lower