If you are a reader to one channel you will automatically be on that channel when you log in.
If you are a reader to more than one channel, every time you log in you will see a menu list of all your channels.
If you are already logged in:
1. Go to 'Menu' at top right corner (iOs) or top left (Android) of your device screen.
2. Click on 'Switch channels'
3. Choose a channel from your channel menu.
4. You are now reading the channel you want.