Assuming nix is installed.
Install direnv:
nix-env -iA nixpkgs.direnv
Follow this setup to hook direnv: https://direnv.net/docs/hook.html
Allow environment script to run
direnv allow
You will be using nix-shell from shell.nix
file in this directory
Build the shell yourself
nix-shell <shell.nix file or empty for the default shell.nix location>