Why handbrake on automatic cars?

There's a lot of ignorance on this, but the handbrake is the parking brake and is used to hold the car stationary. The "park" facility on an automatic is in fact a backup and not intended as the principle means to hold the car. So get your brake fixed, it's usually quite simple.

On an automatic, the handbrake should be used if you park on a hill.

See a mechanic and get the handbrake fixed. The cable could be broken.

Have the handbrake adjusted so it works again. It could be a sign your car needs a lot of regular maintenance you neglected for years. The Camry handbrake is only used as a parking brake, since it is independent from the brake disks. Soon, you should have the parking brake shoes checked for wear. It takes forever to wear them out.

handbrake is a independent parking brake

Probably a cheap fix.

When the hand brake is not used once a week the cables end up seizing in their cable housings. Don't yank them on! The brake will lock up and keep the vehicle from moving.

They were very useful in the days before Antilock Brakes for stopping in slick conditions without losing your steering, still useful if your hydraulic system fails or your parking pawl won't hold.

IT IS A SAFETY PROBLEM PAL! It is a secondary braking system on the rear wheels, get it fixed now!

I noticed that the parking brake on my 93 Camry doesn't work anymore. If I'm in drive and I put it down, it will just keep going. Maybe all you have to do it replace the pads.