How can I really build my confidence?

Today at work I had a performance review with my manager and she was basically telling me that I'm not ready to move to the next level because i'm not assertive and lacking confidence. She said I need to step up and show her I can take charge and be a leader. I just dont think I have what it takes man...My low self esteem is DESTROYING me..my career and my life is at stake and I just DONT KNOW WHAT TO DO ANYMORE 😢😢😩