How do I become more confident and face social situations?

For my whole life, I've been very unconfident, insecure, and self-questioning. I'm super quiet because I'm scared of what people will think of me. I avoid all social situations as it causes me great anxiety. It is how both of my parents have always been, and I feel like I'm doomed to that life also. It makes it super hard for me at work as the other employees try to use me and walk all over me because I'm too nice. It causes me depression and brings me down. I'm in my early twenties, and I really need to create a better life for myself. I've been like this for so long, so how do I change?