How to setup Global Activity page?

1. First, on your WP Admin dashboard, please go to menu Pages >> All Pages. And then please make sure if you already have "Activity" page.

Actually the page should be created automatically if you install Buddypress. But if you don't have it yet, please create a new empty page and name it with "Activity" or any title you want.

2. And then, please go to Settings >> Buddypress >> Pages Tab. And then set Activity Streams to your Activity Page. And "click Save Settings"