Suppose you have four classifications: freshmen (f), sophomore (so), junior (j), and senior (se). You construct a dummy variable, one for each classification that takes on the value of (1) should that classification be true for that observation and 0 otherwise.

Further assume that you estimate the following model:

E[GPA]= .5*ACT+1*So+0.46*J+{c}*Se

How much higher/lower is a Junior's GPA, after controlling for ACT, than for the omitted category?