I feel insecure about my self a lot , when i look in the mirror i feel as if i'm not good enough.i want to change this but have no clue where to start?

At 17 it is normal: o feel this way. You are going through a very chaotic phase in life and in the process doing a lot of work getting to know yourself. Virtually everyone your age feels the way you do even though most will not admit it. I can't take away the struggle but I can tell you that you are more than good enough and you will know that . You can make sure this is the case by simply Doing your best at everything you do and making it a point to help others. Talk with your parents and believe them when they say good things about you. Tell yourself this is a stormy time but you have what it takes to make it through. If you can, volunteer to be a peer counselor at your school.