Final answer:
Mandatory spending is based on existing laws and includes entitlement programs. Discretionary spending can vary from year to year and covers areas like military and education. Interest on debt is the amount the government pays on its debts.
Step-by-step explanation:
Mandatory spending is federal spending that is based on the cost of existing laws and includes entitlement programs like Social Security, Medicare, and Medicaid.
Discretionary spending is federal spending that can vary from year to year and includes areas like military, education, transportation, and veterans benefits.
Interest on debt is the amount of money the government pays on its debt, similar to paying interest on borrowed money.