This exemption limit means that any equity in the property above the limit isn't exempt. In a Chapter 13 case, your unsecured creditors must receive at least the value of your nonexempt property, so you will have to pay your unsecured creditors at least this amount. But this amount is the minimum, by law, that you must pay. If you have little nonexempt property and propose paying back only a small portion or your unsecured debts, those creditors might object to your plan. In some parts of the country, bankruptcy courts may approve Chapter 13 plans in which unsecured creditors receive nothing.
Most courts fall somewhere in between.
Add the amount of missed payments you owe to any secured creditors, such as mortgage or car lenders, whose property you want to keep. Include interest at the rate specified in your contract with the creditor. Some courts require that you add an amount equal to at least three year's worth of interest on the amount in Step 1. This money may be required to compensate creditors for the fact that they're getting their money over a period of years instead of all at once. Total all the figures you've listed.