Three basic proposition-types can occupy either position:
Categorical: “Zayd is present” predicates presence of a subject.
Connected conditional: “If Zayd comes, Amr leaves” relates antecedent and consequent.
Disjunctive: “The number is even or odd” presents alternatives.
A complete instance of any of these can itself occupy a component position within a larger conditional. Hence recognizing a few instances of “if” or “or” is not sufficient: identify which connective determines the outer structure of the whole.