Once you get the money, you cannot borrow further from the loan. You are allowed to borrow up to a certain amount for the life of the loan, a time limit set by the lender. During that time you can withdraw money as you need it. As you pay off the principal, your credit revolves and you can use it again. This gives you more flexibility than a fixed-rate home equity loan.
Credit lines have a variable interest rate that fluctuates over the life of the loan.
Payments will vary depending on the interest rate and how much credit you have used. When the life span of a line of credit has expired everything must be paid off. A lender may or may not allow a renewal. Lenders often require you to take an initial advance when you set up the loan, withdraw a minimum amount each time you dip into it and keep a minimum amount outstanding. The answer to this question is seldom black and white.