U need to have the subscription based Channels DVR server software installed at your source location on a supported device, like a computer, running full time. Channels is a Sever / client based software setup.
The app for the viewer software goes on the client device.
You can use your Comcast login credentials to add a a tuner source, for TVE supported channels.
Or a HDHR Prime Cable Card networked tuner and card rental from Comcast to get all your channel in Channels DVR.
As far a basic remote access to the Channels DVR server, it is a simple toggle in the sever dashboard that opens up access. Though, u may need to setup port forward in your router.
Comcast has their own easy to use app, Xfinity Stream that allows you to access most of your channel line up and access you home DVR from them, if you have the X1 thing.
Perhaps that would be best solution for your needs. I think there is Xfinity app for those devices. and it is a free thing.