Hello. Welcome to Android Central.
Is the GS3 new. Do you mean the Home Screen layout with widgets for some apps. Maybe you have seen multi window on other Samsung Note devices. It is a little annoying that you cannot jump from some open apps to another app like calendar - but sometimes you can.
If you open Calendar for example, hold the Home key where a list of open or recent apps are tiered on the right side.
Let's say it's clear, or you press the right screen button to close running apps.
So now let's start again. Open Calendar and select what you want to have showing (day/ week/ appointment etc).
Long press the home screen, the calendar is showing only, as a mini screen. Touch an empty space in that running apps screen and you're back to the app drawer/list. Select another app you want, say the Chrome browser, chose the browser page you want.
You can now swap between both apps open at the place you want by holding the Home button and selecting either app.
I hope this is what you meant.