When the Odyssey opens, Telemachus is twenty and lost. His father is a story other people tell. The suitors mock him in his own house. He has no authority, no voice, no path.
The first four books — sometimes called the Telemachy — are his coming-of-age. Athena (disguised as Mentor) prods him to leave Ithaca and seek news of his father. He sails to Pylos to ask Nestor, then to Sparta to ask Menelaus and Helen. He hears stories of who his father was, and slowly recognises himself as that man’s son.
By the time Odysseus returns in disguise, Telemachus is ready to fight beside him. The reunion in book 16 — father and son alone in the swineherd’s hut — is one of Homer’s quietest, deepest scenes.