House hacking means buying a home, living in part of it and renting out the rest so the rent covers some or all of your housing cost. The classic version is a duplex, triplex or fourplex where you live in one unit, but renting out spare bedrooms counts too.
Net housing cost = (monthly payment + reserves) minus rent collected
Example: you buy a duplex and live in one side. Your full monthly payment, including taxes and insurance (PITI), is $3,100. The other unit rents for $2,000, and you set aside 10% of that, $200 a month, for repairs and vacancy. Your net housing cost is $3,100 + $200 minus $2,000 = $1,300 a month. If a similar apartment would rent for $1,900, you are paying $600 a month less, before taxes, and you own the building.
Loans for a home you live in commonly allow a smaller down payment and a lower rate than investment property loans. They generally require you to live there, often for at least a year, so confirm the occupancy terms with your lender. The common mistake is judging the deal only while you live in it. Run your numbers in the house hacking calculator, then again as a full rental for the day you move out.