You can surface rivers and buckets to subscribe to in the following ways:-
From the activity stream on your dashboard
Rivers and Buckets either owned or subscribed to by users you follow will appear on your main dashboard
{To be added}
From a user's profile page
You can view rivers and buckets that a user is either managing or following by clicking on their content stream
Through searching
Following a River
Follow a Bucket
Activity on Rivers and Buckets you're subscribed to will now appear on your dashboard.