docs: Add user guide for *Browse and join streams* feature.

templates/zerver/help/index.md

@@ -28,6 +28,7 @@ as a “**realm**”.
 - **[The Zulip browser window](#the-zulip-browser-window)**
 - **[Editing your profile](/help/edit-profile)**
 - **[Create a stream](/help/create-a-stream)**
+- **[Browse and subscribe to streams](/help/manage-streams)**
 - **[Posting and replying](#posting-and-replying)**
 - **[Searching](search-messages)**
 - **[Using emoji in messages](/help/emoji)**

templates/zerver/help/manage-streams.md

@@ -0,0 +1,64 @@
+# Browse and subscribe to streams
+
+On Zulip, users communicate with each other by sending messages to
+conversation streams, which are similar to conversation threads.  New
+users are automatically subscribed to the organization's default
+streams; however, users may want to subscribe to additional streams or
+browse the list of streams that they subscribe to.
+
+## Browse streams
+
+To browse your subscriptions, click the cog
+(![cog](/static/images/help/cog.png)) next to **Streams** in your left
+sidebar. A tooltip labeled **Subscribe, add, or configure streams**
+will appear.
+
+![Browse streams](/static/images/help/streams-1.png)
+
+This will open the stream browser (shown in the following image)
+featuring an overview of all the streams you've subscribed to.
+
+![Streams Overview](/static/images/help/streams-overview.png)
+
+Here, you can explore all the public streams in the organization and
+search for specific streams by entering the stream name in the
+**Filter by stream name** search box.
+
+## Subscribing to streams
+
+Users can choose to subscribe to any public stream in the orgniazation.
+
+### Subscribing when a stream is created
+
+When users create a public stream, they can choose to alert all users
+in the organization about their stream's creation.
+
+Thus, you may be notified about the stream's creation with a message
+in the **Home** view sent by Notification Bot such as the one in the
+following image.
+
+![Streams subscribe alert](/static/images/help/stream-subscribe.png)
+
+The message will present to you the option of subscribing to the stream, and you can do so by simply clicking the gray button.
+
+### Subscribing later
+
+However, if the you were not notified about the stream's creation, you
+can subscribe to a stream by navigating to the stream browser by
+clicking the cog (![cog](/static/images/help/cog.png)) next to
+**Streams** in the left sidebar. Click the **All Streams** tab
+(highlighted in red in the following image) to view all streams in the
+organization, including streams you haven't subscribed to.
+
+![Streams Overview](/static/images/help/stream-overview.png)
+
+Next, click on the area to the left of the stream that you would like
+to subscribe to (highlighted in red).
+
+![Subscribe before](/static/images/help/subscribe-before.png)
+
+A green checkmark will appear next to the stream that you've just
+subscribed to, and you will now be able to read and send messages to
+the stream.
+
+![Subscribe after](/static/images/help/subscribe-after.png)