"man first of all exists, encounters himself, surges up in the world – and defines himself afterwards".
This quote was in reference to the idea of "existence precedes essence". All people are merely existing when they are born – they do not truly have any inherent nature or essence. However, over the course of their lives, they go on to build up their essence through their character-building and their ambitions, goals, decisions etc.
"In fashioning myself, I fashion Man"
Here is a nod to the idea of individuals making "deterministic excuses."Sartre propelled the notion of making decisions with mankind in mind, and indeed, by using the terms ‘I’ and ‘Man’ he has cast a close connection between the two – in that, one is directly affected by the other.