Check out this video for a full overview!
Depending on the situation, both methods can be very useful. Here are steps for both methods
Method 1 - Start from Scratch
Go to the Streams section and scroll until you see the Shared streams section. Then click on the plus bottom
You will then be prompted to create a stream as usual. There is just an extra step to add the people who you would like to share the stream with
Method 2 - Convert a Private Stream into a Shared Stream
To create a shared stream, you first need to create a private stream to share. In the Streams section click on the plus button next to the Private streams.
Finish setting up your stream
Click on the Share button
Add the names/emails of the people who you would like to share the stream with.
Find your shared stream in the Shared section