Zsh

Manual

$ZDOTDIR : Root directory for user level zsh configuration. Usually set to ~
$ZDOTDIR/.zshenv : For setting env variables. This is always read
$ZDOTDIR/.zprofile : Read on login shells. Useful to startup window managers
$ZDOTDIR/.zshrc : Read on interactive shells. This is always read when starting a shell unless -f added
$ZDOTDIR/.zlogin : read at the end of login process. Useful for starting cli daemons/utilities
$ZDOTDIR/.zlogout : read when login shell exits. Can be used to unset variables

Each of these files can have a system-wide counterpart at /etc/zsh

Some cool tips

• Add typeset -U PATH path to your .zshenv or .zshrc to remove duplicates from the PATH variable [Note: zsh auto syncs path with PATH. Hence using -U on both variables]
• ZSH Custom widgets and shortcuts with zle and bindkey