Help & troubleshooting for channels on your Roku device, including adding/removing channels, logging in to, authenticating, or activating a channel, channel-specific playback issues, assistance contacting channel publishers to report issues, and adjusting channel-specific settings.
If you are using a standard desktop monitor, chances are you may be limited to simply watching the Roku Channel as indicated by @renojim by navigating to the link he provided. If you are using a monitor with an HDMI input or using a television with an HDMI input as your monitor, then you can connect a Roku device to it in same manner as your other television and switch from "Display" to "HDMI" to watch the Roku.
Unless you are using dual monitors, you cannot use the Roku and the desktop (for computing) at same time. The desktop portion of the computer cannot/does not factor in to the Roku operation, it is the monitor portion.
Roku Community Streaming Expert Just another Roku user... I am not a Roku employee. Insigna RokuTV, Ultra 4660x, Premiere+ 3921, Express 4k+ 3941