I want to be more mature and secure?

im very insecure, shy, and quiet. im told im pretty but too quiet. i walk around nervously and i just hate it. i wont to feel confident and walk confidently. and im immature because of how i think. i care too much what people say and i compare myself to every girl, i want to be the prettiest but i know im not. i know i cant MAKE myself more mature or secure but how can i try and get there? how can i put out the image that im confident and eventually believe it? how can i walk like a confident person and not be shy?