atcoder-util is both an executable binary that can be run, and a library that can be used in Rust programs.
Installing the command-line executable
Assuming you have Rust/Cargo installed, run this command in a terminal:
cargo install atcoder-util
It will make the atcoder-util command available in your PATH if you've allowed the PATH to be modified when installing Rust. cargo uninstall atcoder-util uninstalls.
Adding atcoder_util library as a dependency
Run this command in a terminal, in your project's directory:
cargo add atcoder-util
To add it manually, edit your project's Cargo.toml file and add to the [dependencies] section:
atcoder-util = "0.3.2"
The atcoder_util library will be automatically available globally.
Read the atcoder_util library documentation.