First, this happens in between chapters 193 and 194 of the manga, so if you are an anime only, there's going to be some mild spoilers:



1) The Symbiote arrives in a small meteorite that falls outside UA, being discovered by Izuku.

2) This Symbiote has a calm and kind personality, explaining to Izuku that he and all his species had been transported to Earth thanks to a strange artifact and even though not all are evil, some Symbiote are somewhat violent and are influenced by the creatures with which they are merge.

3) The Symbiote offers him to merge to not only be prepared if a corrupted Symbiote appears, but also help him control One For All, as many of his kind had the idea of merging with powerful beings to do good together. Izuku thinks about it seriously, but after having had ''the dream'', he decides to accept and thus be able to control his Quirk and protect the people he cares.

4) Izuku decides to give him a name and he calls it Darwin, since he helped evolve as a hero.

5) After becoming one, Izuku's look with Darwin is a combination of Venom and Lasher, one of Venom's ''children''.

6) The only person who knows about the symbiote encounter is All Might, who at first is suprised, but he end up accepting the symbiote.



With this, Izuku will start to train with Darwin to fully control the Symbiote powers, but the question is How long will his friends take to discover what happened?