Each of these words does a part of the program in a reusable subroutine. Words can be called by the interpreter or compiled into larger words. In executing mode, the word's subroutine is run and the interpreter continues with the next token. Tokens not found in the dictionary are converted to a value. If the token is not a valid integer or floating point number, an error is signaled by printing a question mark and the unrecognized token.
Some words place the interpreter into compile mode.
When in compile mode, new words are defined. Words are written into the dictionary as machine language subroutines. Thus, Pocket Forth produces subroutine threaded code. A program is built by factoring an algorithm into its parts, then defining words that assemble those parts into code. None of what is typed is saved, so write programs with an editor.