Here's an easy way to check. Below you should see two images.
The first image is a static checkerboard design (sort of). You don't need Flash to see it.
The second image looks kind of like the first, except it's animated. It moves and spins and zooms and morphs. It's a lot more fun. You can only see it if you have Flash.
(If you don't have Flash, you may see a broken jigsaw symbol instead. Or you may see nothing at all.)
Now you should be able to answer the question:
Do you have Flash?