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Global bash initialization scripts are configured in (configuration.nix)[https://search.nixos.org/options?channel=23.05&show=programs.bash.interactiveShellInit&from=0&size=50&sort=relevance&type=packages&query=programs.bash.].
Otherwise, your home directory is stateful by default. Create files you need and they should "just work" like other distributions
Eventually, one could look in to home manager. Sticking to the stateful environment and learning more about how nix and nix flakes work first will make things easier later without front loading a ton of new things. There are commands to add programs per user.