The most imprtant paper is the offer letter, make sure sign that one and mail it back, so they know you officialy accepted the offer. (your hiring manager will be happy that a new labor will come and you did barging with him before you start. The HR guy will happy that this hiring is done, he do not need schedule interview with othjer candidate. The IT department will start setup phone, and order computer for you if you need a computer)
Other forms can be deliverred to them after you start work. Or call HR ask which form they need right now.
Some company will send you a gift basket with candies, chocolate, wine and flowers after received your signed offer letter...
Feel free ask questions. Please help others if you can in the future....