The title might be a bit exaggerated, but if you have just started your adventure with Erlang I would like to provide you with a couple of hints that can spare you a serious headache.

The basic tool to work with Erlang is its REPL shell, started in terminal mode with erl command. The name REPL comes from read, eval, print, loop cycle and among functional languages is a commonly used term for interactive shell.

Lots of tips/tricks here re: cookies, shell, name/sname, etc. that will save you Erlang headaches.