In one flip, we have a $1/2$ chance of getting heads and winning 3 dollars, and a $1/2$ chance of getting tails and losing two dollars.  So the expected value of one flip is $E = \frac{1}{2}(\$3) + \frac{1}{2}(-\$2) = \$0.50$.
Suppose that we win $\$3$ if we flip a heads on a coin toss, but lose $\$2$ if we flip tails.  What is the expected value, in dollars, of our winnings after one flip?