As mentioned, 3D just gives you perceived depth to images (and does so by using imaging tricks), the Oculus Rift and other such VR headsets will visually put you into the content you're (presumably) playing, giving actual depth to the images displayed.
Basic 3D is more like...multiple "flat" images displayed on different layers. Say you're watching a movie, for example, and there are leaves blowing that appear in front of the characters. Instead of feeling like they're actually there, they feel like they're just on a closer layer to you than the characters are.
VR, on the other hand, gives you an actual depth to the images you see. VR headsets display the information in such a way that it appears as if you're actually seeing the things being display, as if you're actually there. You can really see how far away or how close something is, you feel as if you can interact with everything in the environment, everything looks as it would "in real life".
It's sort of hard to explain to someone who just has an extremely basic idea of what VR is. VR is like 3D on steroids, to such an extent that it's hard to really compare the two. I'd suggest trying to find a store that'd let you try out VR headsets, or even just buying one of those $5 Google Cardboard VR kits that would just give you the idea of what VR is going to be like in order to "get" it.
