This paper is so brilliantly and clearly written that it couldn't possibly need an orientation! ;-)
Read up to section 4. We'll read the rest for next time. Pay particular attention to sections 2.2 and 2.3. Section 2.1 is skimmable. The major concept introduced here (aside from the model itself) is the idea that activity can play more than a single role. The consequences of graded activity playing different roles in cognition help to explain a number of difficult constructs in psychology (consider conciousness for example).