Summarize:

Utility is the "value" or "satisfaction" that a consumer gets from consuming a certain number of goods. A good way of thinking of it is that utility is how much money a consumer would hypothetically pay for the satisfaction provided by a good. For example, let's say that you are hungry and are buying fish to eat for supper. Let's also say that one fish costs $2. If you're so hungry that you would pay $8 for the fish, the fish is said to provide $8 worth of utility. In other words, you're willing to pay $8 to get the satisfaction from the fish no matter what it actually costs. Total utility is just the concept of utility applied to more than one good. If consuming one good gives you a certain amount of utility, consuming more than one of the same good will give you an amount that is higher, lower, or the same. For example, let's say that you plan to eat two fish. However, after eating the first fish, you're not quite as hungry as before. Now, you'd only pay $6 for the extra satisfaction of the second fish. It's not worth as much to you now that you're somewhat full. This means the two fish provide $6 + $8 (first fish) = $14 of "total utility" together. Note that it doesn't matter whether or not you actually buy the second fish. MU is only concerned with what you would pay for it. In real life, economists use complex mathematical models to predict what consumers hypothetically would pay for something. To find MU, you need two different total utility measurements. You'll use the difference between them to make your MU calculation. Let's say that, in the example situation in Step 2, you decide that you're hungry enough to eat four whole fish. After the second fish, you're feeling a little full, so you would only pay about $3 for the next fish. After the third fish, you're almost completely full, so you would only pay $1 for the final fish. The satisfaction you would get from it is almost cancelled out by the feeling of being uncomfortably full. You can say that the four fish provide a total utility of $8 + $6 + $3 + $1 = $18. Divide the difference in total utility over the difference in units. The answer you get will be the marginal utility, or the utility given by each additional unit consumed.In the example situation, you would calculate your MU as follows: $18 - $14 (example from Step 2) = $4 4 (fish) - 2 (fish) = 2 $4/2 = $2 This means that, between the second and the fourth fish, each extra fish is only worth $2 of utility to you. This is an average value; the third fish is actually worth $3 and the fourth is actually worth $1, of course.
Understand the economic concept of utility. Find the total utility from consuming a certain number of goods. Find the total utility from consuming a different number of goods. Calculate MU.