When I was in my teens and 20's, I would use just a light touch around the eyes, perhaps a little color on the cheeks in the evening, and a light, natural color for my lips. I went to a cosmetologist who worked with me to develop the most suitable palette for my skin, depending upon the time of day as well as the seasons. I have always enjoyed using makeup, and I spent many happy moments as a child and as a teen making up my face. I learned how to apply makeup properly,(blend, blend, blend!) but to work out the optimum color scheme, I learned a great deal from a professional. As I aged, my needs changed also, and I once again spent the time and money for assistance from a professional.
You can use as much or as little as you'd like. If I'm running out to the supermarket, I may only apply some lipstick, and walk out the door or I may not apply any makeup at all. If I'm going out for an evening, it will take at least half an hour to properly develop the skin tone that I'd like, apply the color around my eyes, to my lips, cheeks, etc. It depends upon the look that I'd like, if it's a natural everyday look, or an airbrushed, heavily blended more sophisticated appearance. In other words, the amount of makeup that you use is going to be decided by the look that you would like to have for what you're going to be doing and where you will be. Of course, the general rule of thumb is "less is more," and color and application is what is most important. I'm always impressed by a woman who applies her make up, and appears not to be wearing any. It's a look that I very often strive for, and to accomplish that, it takes at least half an hour.
I'm 58 years old. My skin is by far, nothing at all what it was like when I was 18. A lot more time needs to be spent on my look because of the effects of aging, but I can still present a pleasing look in under 15 minutes. It takes practice.
Something that you can do, is to visit the Mary Kay web site,
http://www.marykay.com/. There is a virtual model on the site, where you can choose a face, hair style, hair color, and then you can experiment with all of the Mary Kay makeup products. You can also choose their "makeup artist looks" and see how they look on your virtual face. This allows you, on the computer, to really experiment with many color combinations and overall looks, and of course, they will put everything together for you to purchase. You may find it to be fun. I always enjoy playing with makeup, so I'll try things out on occasion myself.
It's all a personal choice. Makeup doesn't make you a woman.
