Indoor baby portraits

tutster

I am brand new to any of this indoor studio stuff. I have a D3100 with kit lens and a 50mm f/1.8 prime lens. I have been given a cheap studio kit with one backdrop, one light with umbrella and one light to point at the backdrop. I want to take pictures of my 4 month old niece for christmas. Do I need anything else ? Which lens should I use out of the two I have, or can I buy a better one? What settings are best to use? Only one of my lights flashes, do I need them both to flash? If so, how do I do this? So many questions I know! Any help would be very appreciated.
Thank you, Lisa