Home Leave is provided to employees by order of Congress to ensure that Foreign Service employees have the opportunity to spend significant periods of time in the United States while pursuing careers overseas. Home leave accrues at the rate of 15 workdays per calendar year while on overseas assignment, and may be used at the end of a two or three-year assignment abroad, or at the midpoint of a three- or four-year tour. In addition to providing paid home leave, the U.S. government will also pay for you and your family to travel to your home leave address in the United States.
The Home Leave days you accrue are federal workdays, so weekends and Federal Holidays do not count against your HL. All HL must be taken in the United States. You cannot use it for vacations in foreign countries. You may be able to take annual leave, instead, for trips outside of the U.S.
You are required to have a home leave address in the United States. It can be anywhere in the U.S. Many people, who no longer have a personal residence in the U.S., select the address of a family member (for example, someone they would visit while on home leave.) While you will receive your salary during home leave, the Department of State does not pay for housing or per diem during home leave.
Also note that while many of Foreign Service employees accumulate HL days beyond what they are able to use, when you retire or resign you are not compensated in any way for those days. You do not "cash them out" nor are they added to your time in service.