The monthly payments you make will entirely depend on the interest rate and the credit amount you have availed of.
You should pay off the loan when the time limit comes to an end. The lender may let you renew the line of credit or extend the period of payment.
Interest rates are subject to change now and then. You will have to pay more when the interest rates go up.
Your bank will give you a check book by which you can draw against your line of credit. You can use it whenever you want to spend money for a car, a vacation or anything you consider buying.
But you should take care when you use equity lines of credit as your home is on the line. If you spend money carelessly, you may have to lose your valuable home.