I'm new at this...so how do I add more channels?

Hello,
I am new at this Plex server on my Roku player. How do I add more channels even some from other sources? I'm not sure on the process uploading or downloading them into the server. I'm using Ubuntu 16.0.4 as my main OS dual boot and windows 10 on the other end. I do well at following steps I've added some regular channels such as ABC, CBS ans so on. Thank you for your time..