What's "from zero" mean and when's it used?

Native speaker’s answer
Rebecca
If someone does or starts something "from zero," it means to do or start it from a point at which nothing has been done. You do something from the complete beginning. Ex: All my computer data was wiped, so I had to start the project again from zero. Ex: We don't have to start from zero since we have research and notes available. Ex: She started from zero but was able to get to the top position in the game.