N.B.: There are no natural breaks in the text as Plato wrote it, so these notes on the text have been divided artificially, sections beginning or breaking off where a new theme or topic is introduced or dropped. Because page numbers may vary from edition to edition, these sections have been demarcated according to the Stephanus numbers, the page numbers from the 1578 complete works edited by Henri Estienne ("Stephanus" in Latin). The Stephanus numbers are the standard page references in scholarly work on Plato, and most editions of his work contain the Stephanus numbers along the margins.
The dialogue opens with Apollodorus agreeing to tell an unnamed companion who is a rich businessman the famous story of the party held in honor of Agathon to celebrate the success of his first tragedy. Apollodorus retells the account he gave to Glaucon (Plato's half-brother and main interlocutor of the Republic) who had in turn heard of the party from some other, less reliable source. Glaucon had thought Apollodorus had been in attendance, but Apollodorus points out that the party took place many years ago, when he and Glaucon were just children. Apollodorus had heard the story from Aristodemus, one of the guests at the party, and had also checked some of the facts with Socrates himself.
The story begins with Aristodemus encountering Socrates, who has recently bathed and put on sandals--things he rarely does. Aristodemus inquires as to why Socrates is all dressed up, and Socrates answers that he is going to dinner at Agathon's. Agathon's tragedy won him first prize at the Lenaean festival the previous day, and while Socrates shunned the large crowds of yesterday's celebrations, he promised to join Agathon today. Socrates invites Aristodemus to join him, and while Aristodemus is at first hesitant about dropping in uninvited, Socrates persuades him that he must come.
Aristodemus and Socrates head off toward Agathon's together, but Socrates keeps falling behind, lost in thought. Socrates urges Aristodemus to go ahead, saying he will catch up. As a result, Aristodemus arrives at Agathon's without Socrates and is welcomed in alone. Agathon is delighted to see him, saying that he was looking for him yesterday so as to invite him. Aristodemus explains that he came upon Socrates' invitation, and is surprised to find that Socrates has not caught up with him. Agathon sends out a slave to find him, and the slave returns, reporting that Socrates is standing on a neighbor's porch and will not come in. Agathon orders the slave to go and fetch him in, but Aristodemus insists that Socrates be left alone: he will come of his own accord when he has finished thinking.
Aristodemus joins the other guests and they begin eating. Among those assembled, there is the young Phaedrus, Agathon's life-partner Pausanias, a doctor named Eryximachus, and the great comic playwright Aristophanes. The meal is halfway over by the time Socrates finally appears. Agathon encourages Socrates to join him on his couch so that he may share in the wisdom that came to Socrates on the neighboring porch. Socrates remarks that if wisdom could flow freely from the wiser to the less wise, Socrates should be the one benefiting from sitting near Agathon. Noting the mocking tone in Socrates' voice, Agathon suggests they might test one another's wisdom later that evening.
After dinner, Pausanias takes responsibility for organizing the drinking. All the guests but Socrates have participated in the wild revelry of the previous night and are feeling rather hung over. Eryximachus recommends that they not drink too much this evening in the interests of their health. He suggests further that they send away the flute-girl, who was to be their entertainment, and engage instead in conversation. He had been speaking recently to Phaedrus, who had lamented that the poets compose songs of praise to all the gods but Love. Consequently, Eryximachus recommends that each person present, starting with Phaedrus, make the finest speech he can in praise of Love.
You do not have to look outside you as everything is in your "self", everybody is the two energies (woman-man/yin-yang/...) and if you awaken your "opposite" you are "one", you are realized, totally happy. This is called e.g. in the Bible the Holy or Mystic Marriage. Also the alchemists describe it as "Coniunctio Oppositorum", the Philosopher's Stone, make Gold from Lead,... See the writings of the Mystics too. Etc.