On soap operas & movie sets, they use hot rollers for volume & curling irons. My friend is a makeup artist.
On soaps, they like to set all the women's hair first thing in the morning, then while still in rollers, the gals go to have their makeup done. This way they can accomplish two things at once and not wait till the hair is finished. Once makeup is done, they are off to wardrobe, They get dressed, and they are back to get their hair combed out, fluffed, sprayed, etc. Usually hair is done last, so the poof remains, right before shooting.
I have three different sizes circumferences of curling irons, to get the look I want. Skinny for spiral curls, Medium for larger curls, like I would get with hot rollers, and a 2 1/2" round, jumbo, for just a flip at the ends, or I also use it to straighten my hair, instead of a flat iron. (I do end up with a slight flip at the ends.)
To use a curling iron, you grab about a 1 1/2" section of dry hair, run the curling iron down the whole shaft. Lightly put some pressure on the clamp part, so it has some slack while doing this and the hair slides through the clamp & iron. When you get to the end, you roll up the hair a couple or few times, depending on how much curl you want.
Let it heat up for about 30-45 seconds. If you smell burning hair, you are heating for too long!

Press the clamp, and slide the curling iron out of the curl, withOUT unwinding the curl. Don't touch the curl. Let it cool in position, as you move onto a new section. Once you are done with the whole head, you can go back & touch up spots or brush out.
If you want spiral curls, take a 1" section, twist it so it looks like a rope. Place the iron at the end of the hair and twist the whole rope around the curling iron tightly, making sure the whole rope is getting heated. Heat for only about 30-45 seconds & again, slide out the iron without unwinding the curl.
The best curling irons have a steam feature, that locks in the curl as the hair heats up, then dries while being ironed. I've also seen the hairdressers spray each section of hair with a heat styling product before curling. They do this with both the hot rollers or the iron.
Once, when I was visiting my makeup artist friend on set, and they cast had gone off on some location shoot & we had to wait for them to come back. (Not all the hair & makeup people had to go with them. No room on the bus.) One of the gals played with my hair. She sprayed my stick straight hair with Paul Mitchell's Heat Set and did my whole hair into tight spiral curls. The humidity had to have been 98% and it was 89 degrees out. My hair held up & stayed curly.

I even slept on it and the curls lasted overnight! I was quite impressed.