Affiliation with french social security

Hello everybody,

I am Amalia from Romania and I just got a job offer în Paris and I will have to start work on the 1st of April.
I asked what papers should I gather/get ready to present on my first day and one of them is an affiliation with french social security. I am kinda lost with that and I would appreciate any help, links, starting point advice. I dont know from where to start the process , where should I call, what is the official link for that. I have to say that I dont have a place selected yet as an address or bank account nor am I în France at this point. I have to end my notice period where I live so I cant be present  în Paris for now but I will arrive 5 days before the starting date. How long is the process to get the social security number i guess?
Thank you very much în advance for any input.
Kind regards,
Amalia