what is the difference between substitution and condensaiton

Substitution is a reaction in which an atom or a group of atoms
is/are replaced by another atom or a group of atoms such as
substitution reaction of CH3Br + HCN→ CH3CN + Br-.

For condensation reaction, a small molecule such as water will
be formed. One of the examples is the esterification in which
heating ethanol with ethanoic acid to give ester with water
molecules formed. Esterification is a condensation reaction.

Substitution involves atoms comparing condensation involving
Small molecules.