I didn't know how to use makeup either (my mom rarely uses makeup, and then it's only some lipstick and mascara). I just basically taught myself from the internet and trial and error.
I wish I could find the link, but there was an article in Real Simple (the magazine) that was really helpful. They have a lot of good articles on makeup & beauty basics.
What I'd do:
-start with the skin. Wash it daily and treat pimples (I have super oily, acne prone skin--gross). If the skin underneath is good, the makeup will look all the better (and usually the more you try to hide something, it's obvious that you are trying to hide it). I personally use a concealer stick here and there and dust on some powder and I'm done. I'd recommend powder--you use much less of it than liquid. However, if you have dry skin, the oils in liquid may help you.
-use mascara and a neutral eye shadow. I don't use eye shadow because my skin is so darn oily, but I always wear mascara (on the top lashes only). I wear eyeliner occasionally--for a more natural look use a stick and only line the top lid.
-wear a neutral color lip gloss or lipstick. Also don't ever throw away a tube of lipgloss/stick if you don't like it at first. You can layer it with another color and voila 'new' lip gloss!
Youtube and Google were my friend in discovering how to do makeup. And yes, when you are first starting out, you will buy some colors thinking they will look good and when you get home and try them on, they will be awful. So be prepared to waste some money. I stick with drugstore brands, so it's not a lot when I do mess up.
It is helpful to know if you have a cool or warm skin tone. Think about it: what colors do you look good in? I'm have a cool skin tone and look good in pinks, maroons, blues, etc. I cannot wear yellow or orange to save my life--I look like a corpse (those are colors that look good in warm skin tones). I've heard that if you look at the veins underneath your forearm and they are blue=cool skin tone and if they are green=warm skin tone.
And you could just follow everyone else's advice and get a makeup consultation. I've never had one, but I'm sure they could give you some good ideas.
