The web app viewing area is found by using the left menu top section switcher - select Viewer on the switcher. If you only have viewing rights then the web app will default to the viewing area after project selection.
Note for admins - by default to create more space for viewing the menu may automatically minimise when you navigate to the viwer. You can expand it using the bottom left arrows and you can still switch sections by clicking where the minised section switcher says Viewer.
Grid and Switcher modes
The viewer has two different ways of viewing - Grid or Switcher.
You can change between the modes by selecting the layout button at the top right of the interface. It has two different looks depending on what mode you are currently in.
Grid mode
Grid mode will form a grid of all available programs and default to Auto Grid which will lay out the grid to fit all programs possible. There is a maximum of 9 programs so if the channel has more then the grid will paginate with numbered pages underneath it.
You can override the grid at any time by selecting a different grid size. if you resize to a layout that has less players than there is programs then it will paginate the grid and place pagination controls under it.
Note that the grid icon itself also represents your current grid layout where solid rectangles are the current layout eg 1x1, 2x2 or 3x3.
Switcher Mode
Switcher mode allows you to have one large player and a selection of smaller preview players underneath. If the number of programs is larger than the amount of smaller previews that can fit under the main player then the smaller preview players will be paginated with controls for pagination under them.
Clicking on a preview will switch the main player to that program.
Auto Solo and layout modes
Auto Solo audio works with Grid and Bottom Bar modes. When Auto Solo is turned on for Audio then whichever player is selected will currently solo on the audio and will override any other mixer settings for solo or mute.
Note - audio must be 'started' and not muted for Auto Solo to work
Channel video settings
The Channel video settings button is a cog icon on the top bar 
Once clicked it will present Quality and Buffer settings.
Quality
Quality will default to ABR or 'Adaptive Bit Rate' mode where simultaneous streams are packaged into a single program. These are only created if Transcoding is turned on for the project and the various FHD and HD settings are also turned on in the Project Settings.
By default transcoding will create 1080p, 720p, 540p and 360p. When set to AUTO it each player will adapt as it sees fit to keep the stream going with minimal interruptions. You can override the AUTO mode and select any of the above resolutions if available. All programs will then adhere to this new setting. Any changes made are stored locally in your browser and will remain if you navigate away and return later.
You can override the global Channel settings of each player individually so it is set to it's own value. Hover over the player and click the cog icon at the bottom of the overlay controls that show when hovering. Click it and choose Customand it will then present options for this player. If you want it to adhere to global Channel settings then click Default.
It is worth noting that currently Custom settings for each player do no survive navigating away from the viewer or a page refresh and will switch back to Default global Channel settings.