The command to output a string in Tcl is the 'puts' command.
A single unit of text after the puts command will be printed to the
standard output device (in this case, the lower window). The default
behavior is to move the cursor to the beginning of the next line after
printing out a line of text, instead of leaving the cursor at the end
of the text.
If the string has more than one word, you must enclose the string in quotes or braces ({}). A set of words enclosed in quotes or braces is treated as a single unit, while words separated by whitespace are treated as multiple arguments to the command. Quotes and braces can both be used to group several words into a single unit, however, their behavior isn't identical. In the next lesson you'll start to learn some of the differences between their behaviors.
If you do not enclose a string in braces or quotes, then the string will
be interpreted as several arguments instead of as one argument. Many
commands in Tcl (including puts) can accept multiple
arguments. If the string is not enclosed in quotes or braces, then the
separate words in the command will interpreted as separate arguments, by the
Tcl interpreter, which will pass the argument to the puts command.
The puts will try to evaluate these words as optional arguments,
which will probably result in an error.
A command in Tcl is a list of words terminated by a newline or
semicolon. Comments in Tcl have a # in the position where a command
could be. Some commands in Tcl may contain multiple words, so in order
to put a comment on a line after a command the comment must be preceded
by a semi-colon, to terminate the command.
My personal style is to always use the ;# for comments.
For now, run the example, and try modifying the string a little to get
familiar with the tutorial system, and running scripts. When you are
comfortable with the puts command, click Next Lesson to continue.