What is highlighter?
Highlighter comes in many ways, there is powder highlighter, liquid or cream highlighter, stick highlighter and a couple more. Some are used differently but for the most part they are all the same.
For example, liquid or creams can go under the foundation or over it while it's still wet, where powder goes on top of your foundation after everything is done. But also, there are no rules to makeup so whatever you like best, do it!
Highlighting your face creates an illusion that light is hitting that part of your face. A lot of people use this trick to make their cheekbones appear higher, eyes to look bigger, nose to look slimmer, etc.
Highlighting can make you appear younger and luminous which is amazing but you definitely don't want to over do it because you will risk looking oily and too shiny or sparkly, but if that's what you like then by all means, go crazy!
Highlighting usually goes best when you also contour but you definitely don’t have to do it.
Here are some places to apply it:
Top of your cheeks for higher cheekbones
Inner corner of your eye and/or under your brow bone to create brighter and “awake” eyes
Bridge and tip of the nose to make it appear slimmer
Your cupid's bow to make your lips appear bigger and for your lipstick to appear nice and clean