Adderall's an amphetamine. XR = extended release, so the dose releases over time instead of all at once (lasts longer, less powerful @ same dose).

In general, the effects are like the street drug speed, albeit less intense. It makes your mind race, imparts the urge to get stuff done (good for homework and the like, which is why it's a popular study drug), and generally makes you feel 'tweaky.' It's not euphoric, so it's not a very popular recreational drug, but some use it this way anyway (usually at higher doses than 5MG XR). Many who do report that smoking pot at the same time makes it a lot more fun; others say this is not a very good combination. YMMV.