Also you must set up the N300 with the details of your connection to your ISP in the N300. There is a setup wizard ,or you can do it manually.
Before you do anything, you'll want to get a manual for both devices; and work out exactly what you need to do. Knowing how to reset your Speedstream and reestablish a working internet connection (before trying anything) would be a MUST - in case you mess up getting into bridge mode and need to reset your Speedstream and set it back up with a working internet connection.
Once you have a working, wired, internet connection thru the N300, you can go back and setup your wireless network.
Don't forget to change your N300's default password
For every Netgear router I've owned, the way to login was to type 192.168.1.1 into your web browser address bar. The default user name and passwords were "admin" and "password".