In order to know how much your security deposit is, check the electronic lease document that was sent to your email via DocuSign.
Your payment for both the security deposit and pro-rated first month's rent are due 24 hours after your new lease is signed by both you and the lessee. This is standard as your lease is a legal contract at the point of signing.
Both payments can be submitted online via your resident dashboard. See this article to learn how to make payments online.