In the first part of his defence Socrates relates the story of Chaerephon, who was told by the Oracle of Delphi that no one was wiser than Socrates.
This presents a problem for Socrates who thought that he was not wise at all. The Oracle is the voice of the God Apollo and thus has to be right.
Socrates then goes to those who are allegedly wise, to test their wisdom. He engages them in conversations and questions them on their areas of alleged wisdom.
These form the basis for the Platonic dialogues. However, Socrates does not find anyone who is actually wise and in most cases finds that they do not know what they are talking about.
Thus, Socrates states that he is wiser only in knowing that he does not know. According to Socrates, wisdom lies in the acknowledgement of ones ignorance. True wisdom is only available to the gods, while the wisdom present in humans was only a realisation of this fact.
Thus Socrates never actually claims to be wise, but instead claims to be a lover of wisdom â€” from where the word philosopher is derived from. Socrates believed that his mission from the Gods was to expose the vanity of human intelligence by showing incoherencies in the arguments of the alleged wise.
Socrates explains he did not have the answers to the questions he himself asked, but posed questions to pursue better and more coherent knowledge.