\documentstyle[doublespace]{report}but you wanted to use 12pt type (10pt is the default), you would change it to:
\documentstyle[doublespace,12pt]{report}NOTE: Be sure not to put any spaces in the above line. For example, [doublespace, 12pt] will not work.
\tinyThe case is important in these commands. Also, in some document styles, some of these commands may produce the same size font. For example, if you wanted to just make a small part of your text in a different font, you would use something like:
\scriptsize
\footnotesize
\small
\normalsize
\large
\Large
\LARGE
\huge
\Huge
This is in normal text, while these words are in {\large large text}.Or, if you wanted to put a larger region in a different size, you'd use something like:
\begin{small}
this will all be in small text
this too.
etc..
\end{small}