I started wearing makeup when I was almost 15, and boy did I suck at applying it! I would wear dark brown eyeshadow, which looked terrible against my brown eyes, along with way too much mascara and black eyeliner. I also wore heavy foundation that was at least 3 shades too dark, and I didn't even bother to try and blend it down my neck! Definitely start small, just use a few products that are natural looking! Brown mascara and brown eyeliner (just a thin line, try not to make it too thick) should be fine, if you want to wear eyeshadow make sure it's not too dark or too bright, and if you choose to wear foundation, definitely make sure it matches your skin tone and looks good in any lighting! For lips, go with clear or tinted (but close to your natural lip shade) lip balm or lip gloss to start with.
One last piece of advice: never think of makeup as a tool to cover your flaws, think of it as a tool to enhance your already beautiful face!