First thing about baking a scratch cake is, don't freak out, it is not as scary as it seems!
With cooking "a little of this and a little of that" works well. However, in baking, it is important to measure your ingredients carefully. Fill a measuring cup with flour, don't shake or tap it, and run a straight edge over the top. If it says to sift, or to mix dry ingredients in a separate bowl, do it.
Just relax, and have fun with it. Start with a very basic recipe first - I would actually suggest doing a chocolate cake first rather than a white one.
If you need recipes, just check out the cakes forum here! There are many TNT ones to choose from.