I just bought a SpeedStream 4100 modem

most of the 2wire model are modem router , so there is no need for you to connect ur speedstream modem with ur 2wire .. verify connectivity to the internet using hardwired cx with ur 2wire first before trying to use wireless . ..

if you brought the wireless new from a vendor. you don't need to configure it. unless you want to.
but if you brought a used one (in you case). you have to configure it. You need to get inside (software wise) of the modem. to do that you need login name and password to start with. if you don't have it, please call or e-mail the guy you brought the modem from.
then you have to configure the security for the wireless, unless you want everyone under sun to access your modem via wireless.
search on the web, you should come away with a user manual for the unit.