To use tabs, you want to use the "tabbing" environment.  (This is all
described on page 62 of the latex book).  It's probably easiest to explain
this by example:

	\begin{tabbing}
	If \= it's raining \\
	\> then \= put on boots,\\
	\> \> take hat;\\
	\> or \> smile. \\
	Leave house.
	\end{tabbing}

This would produce:

	If it's raining
	   then put on boots
	        take hat;
	   or   smile.
	Leave house.

Tab stops are set with the \= command, and \> moves to the next tab stop.
Lines are separted by the \\ command.

Here are some of the other commands that are available in this environment:

  \+   Causes left margin of subsequent lines to be indented one tab stop
       to the right, just as if a \> command were added to the beginning
       of subsequent lines.
  \-   Undoes the effect of a previous \+.
  \'   Indents text flush right against the next tab stop.

For a full description of all the commands available in this environment, see
Section C.9.1 of the LaTeX manual.