Adding programs/would like to add the Today Show, and Nightly News, both NBC

You can do a search either on the Roku store or your app or google and see what app is required to watch those shows.   You can search by show name as well as search NBC channels.  There is an NBC app which may have what you are looking for or possibly Peacock or a variation of streaming services such as Fubo, Hulu, etc... or cable/sat providers, such as Comcast, Charter, DirectTV...etc that you can subscribe as part of a streaming package.  

Or you may be able to find local NBC channels broadcast live on the various free services, such as Roku Channel and others. 

I cannot say one way or another since I use a streaming package, but there may or may not be a subscription required to watch live broadcast of those shows on a daily basis, depending on what services you have.

You may also be able to watch over the air broadcasts as well via an antenna, depending on your location.