You launch Planck by typing planck in a terminal.

If you'd like to get help on the command line arguments to Planck, do

planck -h

The command line arguments to Planck are heavily modeled after the ones available for the Clojure REPL. In particular, you can provide zero or more init-opt arguments, followed by an optional main-opt argument, followed by zero or more arg arguments. Planck also accepts long arguments (preceeded by two dashes), just like the Clojure REPL.