Curling Irons / Flat Irons: Similar to hot rollers, curling irons and flat irons use heat (and in the case of curling irons, occasionally a little moisture) to change the curl pattern of the hair. The main difference is that the curling iron lets you add curl in specific places (the flat iron let's you straighten target sections of the hair). You can style your hair in a myriad of ways and then use the curling iron to add curls only where you want them, or use the flat iron to give a smooth sleek finish. Curling irons come in a variety of sizes from tiny, pencil-thin barrels for tight spirals, to large barrels for big soft curls. Similarly, flat irons come in varying widths to give finer control. Generally, the longer your hair is, the larger the curling iron you want to use. With flat irons, the larger the heating surfaces on the flat iron, the larger the segment that can be straightened will be.
Number 1: Curling irons only work well on completely dry hair. If your hair is even a little damp, the resulting curls will be limp, if they manage to hold at all. (Using a flat-iron on still-damp hair only serves to swell the hair shaft. Applying the concentrated heat of the flat iron's elements onto the damp hair basically "cooks" the hair, and can seriously damage it.)
Number 2:Curls formed using a curling iron must be allowed to cool fully before they are manipulated further. (Likewise, segments straightened with a flat iron should be left to cool to prevent reversion to the previous curl pattern.) Wrap the segment of hair around the curling iron barrel, hold the tool in place for a few seconds to evenly heat the hair, then gently slide the barrel out of the curl and allow it to sit in place until it cools.
Number 3: Lightly misting the segment of hair with hairspray will give a stronger hold to the resulting curl, or will help to eliminate frizz in flat-iron styles.