When setting the channel availability, you can choose to have it always available, available after or before a certain date/time, or available between two dates and times. Whatever setting you have this at will be the window attendees will be able to access the channel. However, you may also set the content within that channel to be available at different times (more below under Content Availability). Doing this will allow attendees to access the channel and see what content is upcoming within the channel without allowing them to access the videos under each content until you are ready.
Alternatively, you have the option to make the channel private. By doing this, it prevents the channel from being accessed without a direct link. This means it wouldn't be accessible through a search engine, you would need to send out the URL to get to it. Having the channel private is beneficial for when you need to test out the stream or simulated live stream before you make it available to the public.
Under channel availability, you can also connect the channel to a Brushfire event. You can find more information on how to do this here.
The content availability has the same features as the channel availability above, you are able to select the date/times you want the content to be available as well as set it to be private. However, you are also able to restrict user access by attendee types or attendee fields from the event the channel is connected to. When you connect a channel to the event, you can choose the attendee fields that will have access to the channel, under content you can select different attendee types.
For instance, if you want all of your attendee types to have access to the channel but you have a video stream you only want one of those ticket types to be able to see, you can set that under the content availability. You can also go one step further and only allow access to attendees who answered a specific question on their registration form (great for breakout session selection, for example).