Not sure what you are saying? Each are separate apps. You just exit out (or hit the HOME key) to get back to the home screen and open the other one. Each one is independent.
If at all possible, do NOT subscribe through Roku. Always subscribe directly at the service's web site. This gives you the most flexibility to use any device you want. The WORST way is to subscribe through The Roku Channel, as that will only work through that, and sometimes doesn't match the same content availability.