There are a lot of products out there for your hair, all claiming to give you the perfect hold for your style. The truth is that not all hair is created equal, so what works for your best friend's long, curly hair will probably not give you a great result in your short, straight hair. Here's a survey of your basic hair products and what they do so that you can decide what you need.
Hair spray is best for finishing styles or for getting things to hold while you're styling. For example, if you're trying to curl your hair with a curling iron or curlers, spraying a little hair spray on the strands or all over your head can make it easier to get the curl to hold, and spraying it all over when you're done with a curl job or an updo will help it to set. However, beware--if you don't hold the hair spray away from the hair a little way, you'll end up with stiff, sticky hair.
Hair spray ISN'T so great as the main product for taming natural curls or for straightening. It won't deal with the frizz problems of curly hair, and for straight hair it will just make hair that should flow look sticky. Unless you need something to finish the overall look created by other products, don't bother.
Mousse is a good option for people who want a very light base for creating body or curls. Some mousse will work for controlling natural curls, but it won't work for more frizzy, harder-to-control hair-types. The nice thing about mousse is that it's much easier to keep looking natural. Use it on slightly wet hair for the best results, and make sure to rub your hands together to keep it from getting too concentrated and sticky in one area.
Pomade can be tricky, but it's a great option for many hair styles, and not just for spiky ones.
Some pomades are waxy or gluey, and they work best for people who want to create spikes or more defined looks that require some hardening. However, there are also cream-based pomades work well for less defined hair styles, like choppy bobs or even feathery short cuts. Just rub a little on your hands so that it won't clump or make your hair greasy, and then work it carefully into the ends or your dry hair to add shape and definition to your style or to control frizz. You may want to finish this look with a light spray to keep it the way you want it, or you may want to shake your head to keep make it fall down more naturally.
Gel is similar to pomade in some ways, but it's a little more sticky and a little less greasy. It works better on wet hair than pomade and can keep a wet look in your hair. It's a good option for people who struggle with their curly hair - they can put in some curling gel and use a diffuser to get their hair to curl in a defined way instead of as a mass of frizz. With pomade, gel is one of the best options for men's hair as well, especially if they want to create spikes and separate pieces.
Glaze is light and lotiony, so it's great for fine hair and for more manageable curly hair that just needs a little tone-down on the frizz side. It works well in dry hair and in wet hair, and unlike gel, if it air dries in wet hair, it won't dry stiff.
The important thing is to be acquainted with what your hair does and how it feels so that you can pick products that will help your hair instead of weighing it down. Don't use a product just because your friend does, unless the two of you have the same hair type and style.