Brake master cylinder is bad

For starters here is a guide that will help with replacing it:

https://www.2carpros.com/articles/how-to-replace-a-brake-master-cylinder

Also, you are going to have to bleed the brakes so here is a guide that will help with this:

https://www.2carpros.com/articles/how-to-bleed-or-flush-a-car-brake-system

Below you will find the process from the manual. Please let us know if you have other questions. Thanks