Yes, Ali, you've left a couple of confused girls over here. I'll take a stab at this one, Ms Grace, and since I know nothing about carpentry I'll take the other tack!
Ali, if you don't know your size, or what will suit you, the best thing is to accompany a sister if you have one, or else a friend of approximately your size.
Go to some of the larger and more informal stores where the staff don't follow you around. Let your friend select the clothes, with some of your assistance, and accompany her (as the boyfriend

) to the changerooms. You'll quickly find what sizes you will need and what clothing will suit you.
It would help to understand your body type before you go shopping, so that you select things that are likely to favour you. There are many websites which explain this.
Ah, and I'm assuming your talking about M2F, and since you don't tell us anything about you...