Both loan types allow you to access your home equity, but there are big differences. A home equity loan gives you a lump sum at a fixed rate with fixed monthly payments for a set term. If you need additional money, you'll need to apply for a new loan. Some home equity loan borrowers request more money than they think they need to avoid having to go through the application process again.
HELOCs usually have a variable interest rate, with payments based on how much you've borrowed. If you don't borrow any money, you don't have to pay any interest. You can borrow as much or as little of your HELOC credit limit as you like. As you repay your HELOC, you increase your available credit for future borrowing, similar to how a credit card works. When the initial draw period ends (the time when you can withdraw money and only make interest-only payments), your outstanding balance turns into a term loan similar to a home equity loan.