Sartre believes that because we have no clear purpose at the start of life or a clear creator, we are free to choose our own destiny. Rather than being a product of the actions of another, a person can choose to develop their own interests and select different paths in their life. Many man-made objects has a predestined purpose, and people can discern this purpose through its appearance and function. The same cannot be said about a human. The only thing you can describe about a human is their appearance; anything else - interests, hobbies, career, etc. - remains uncertain until they explicitly state it.
‘Anguish’ to Sarter means the anxiety that comes from making decisions without any help. Because humans have absolute freedom regarding their
