What this does: Any page you're on... click the button. You now have your current page split with Google search. I strongly strongly recommend that you steal this and put it on your site, so you can use it and modify it for your own search engine. I don't want to know your search history.
What you might use it for: tech support, research, general lookups.
Drag SideBy Google to your "Links" Toolbar.
IE users who can't drag might need to right-click on the link, Add to Favorites, [Create in] Links.
If you want to point to your own site:
1) get the source from here
2) change the drag link to your .html location.