How do I access channels on Roku?

I'm curious, how exactly do I go about accessing channels on Roku? I've heard about its vast library of content but I'm not sure where to start. Could you guide me through the process step-by-step? Is it a simple matter of navigating through the Roku interface, or do I need to take any additional steps to access the channels I want to watch? I'd really appreciate your help in understanding this process.