There are 3 options to attach flash to your Canon 7 camera.
Option 1: Attach the Canon dedicated flash by the side bayonet mount. These vintage flashes are fairly easy to find, but quit a hassle to use. And you need to buy bulbs for them.
Option 2: Use the flash adapter that converts the side bayonet mount into a hot shoe. Attach a regular hot shot flash and plug the sync cable to the body. The mount flash will be slightly off center.
Option 3: Use the hot shoe adapter that converts the side bayonet mount into a hot shoe. Like option two, but this one mounts a hot shoe directly in the centre of the camera. The flash will be mounted at the center of the camera and connected via sync cable. This accessory is expensive and hard to find.
Hope that helps.
Cheers,