What is used to hold the hijab in place?
Sometimes just a bonnet (or velvet headband) is enough to hold it in place.
There are also magnets that go under your chin to help hold in place that way. Others will use a safety pin for the same effect.
Other times people prefer sewing needles, called hijab pins, to place carefully. Basically these are straight needles that weave in and out of the the hijab and under cap (bonnet) to keep everything in place.
Some people use an under cap (bonnet) and others don’t. It depends on personal preference, material of the scarf, and comfort. Most turban styles do not need anything to secure as they hold themselves.
Personally, I use an under cap for chiffon or silk scarves. I almost always use a magnet under my chin unless it’s a windy day and then I add one straight pin at the top of my head.