@Yvonne19601: If you swipe from the top of your screen to the bottom, then swipe down again to maximise the Quick Settings menu you should see an option called 'Auto Rotate'. At this point, turn the tablet so it is in Landscape mode, then tap the Auto Rotate option so it locks (padlock symbol). This will lock the device in Landscape, however please be aware that the some apps only work in Portrait mode. Hope this helps.
