This is the 3225th most frequent German word.
f
The letter "f" in German is simply the sixth letter of the alphabet and corresponds to the same letter in English.
Here, 'Fisch' is a noun referring to food, specifically fish.
Frank hat heute Fisch gegessen.
Frank ate fish today.
In this sentence, 'Fortschritt' is a noun meaning progress, and 'F' indicates the first letter of a word starting with 'F'.
Der Fortschritt in der Forschung ist bemerkenswert.
The progress in research is remarkable.
The term 'Feuerwehr' means fire department, and 'Feuer' means fire, both containing 'F' as the leading letter.