There are different Usages of the letter F.
1. the sixth letter of the English alphabet
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
This letter denotes the next after E in a set of items, categories, sizes, etc. e.g. It also denotes the sixth of six or more hypothetical people or things. It also denotes the sixth highest class or the lowest of academic marks as Fail.
2. Music Chess
In Music it denotes the fourth note of the diatonic scale of C major. And, in Chess, it denotes the sixth file from the left, as viewed from White's side of the board.
F = Fahrenheit while denoting temperature. F = Female. F = Fine, while grading pencil lead. In motor racing as F1 Motor Race, here F = Formula. Besides, B letter of English Alphabet is used in France as International Vehicle Registration.
F is a symbol of Element Fluorine and in Physics F = Farad which is the SI unit of Electric Capacitance that equals to the capacitance of a capacitor in which one coulomb of charge causes a potential difference of one volt. F as f = Frequency that is the rate at which something occurs over a particular period of time.
the Big F which represents a Big Mess. Apparently, F is abusive word here.
The most Common Noun which is used to learn this letter at the Nursery level is Fish; F for Fish.