Dotfiles are all the hidden settings and configuration files you have on your unix system.
I wrote a bit on how you can set up and start customising your shell from scratch as well as how to set up a dotfiles folder and share it on GitHub here.
My own dotfiles can be found here. They are always in that state of flux. But I am learning and adapting things as I go.
I also document my dotfiles repo structure as a map here.