Source code text is typed from the keyboard, pasted from the clipboard or loaded from a file. The text is interpreted one line at a time. When the line is completed an 'ok' prompt appears and the input sequence restarts. Tokens are any group of characters, excluding space, tab and carriage return. Individual tokens are separated from each other by one or more spaces.
Carriage return signals the end of the line.
Each token of a line is looked up in a dictionary. The dictionary is a list of named subroutines, called words. 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.