I would like to replace the activity stream in the sidebar with my own content. How do I do this?

I am new to Vbulletin v5.6.4 (upgrade from 4.2.5), so I'm slowly learning where things are. I'm finding that I generate a lot of errors when I use SiteBuilder, even things like the page background color. The whole site went thud when I tried to replace the activity stream. Is there a specific format I need to use?

I tried to edit the "Welcome" block and it disappeared...