Compiler design unit 1 notes

How do you find the first function in compiler design?
Rules to find First()
If X is a terminal, then First(X) is {X}.
If X is a non-terminal and X tends to aα is production, then add 'a' to the first of X. if X-\x26gt;ε, then add null to the First(X).
If X_\x26gt;YZ then if First(Y)=ε, then First(X) = { First(Y)-ε} U First(Z)..
What is first in compiler design?
The First set is a set of terminal symbols that can appear as the first symbol of a product derived from a nonterminal symbol.
The Follow set is a set of terminal symbols that can appear immediately after a nonterminal symbol in any derivation of the grammar..

How do you find the first function in compiler design?