If you are using the revBrowser feature you would do something like this:
Button 1 Script
on mouseUp
Launch url "http://www.google.com" // Opens in users default browser
end mouseUp
Button 2 Script
on mouseUp
go to card "browser" // name of your card with the browser on it
end mouseUp
Card "browser" Script
on openCard
revBrowserNavigate instanceId, "http://www.google.com" // Opens URL in browser instance
end openCard
If you're writing a mobile app and using the native browser object there you'll want a slightly different card script:
on openCard
mobileControlSet controlID, "url", "http://www.google.com"
end openCard