の has two common N5 uses. It links a noun to another noun to show possession or a relationship, similar to “of” or the English possessive: 私のかばん means “my bag.” It can also turn a verb or adjective clause into a noun-like phrase, often meaning “doing something,” “the act of,” or “the one that is [adjective].” With a na-adjective, な comes before の. の itself is not a polite or familiar ending; the politeness of the full sentence comes from the predicate that follows it.