You do not have to use LaTeX, use MonsterWriter instead!

LaTeX Font Size

1. Configuring the Latex Font Size for the Whole Document

In order to change the size for the whole document you specify the size in pt within the document class (see first line in Listing 1).

\documentclass[10pt]{article}

\begin{document}
Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy
eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam
voluptua. At vero eos et accusam et justo duo dolores et ea rebum.

At vero eos et accusam et justo duo dolores et ea rebum. Stet clita
kasd gubergren, no sea takimata sanctus est Lorem ipsum dolor sit amet.
\end{document}
Listing 1 - Using the article documentclass with font size 10pt
Comparing the LaTeX generated document with 10 vs 12 pt
Figure 1 - The resulting PDF configure with 10pt font size on the left side and with 12pt on the right site.

Most LaTeX document classes support 10pt, 11pt or 12pt as a font size configuration. If you use an unsupported font size you will get the warning shown in listing 2. In this case LaTeX will fall back to the default configuration.

LaTeX Warning: Unused global option(s):
[14pt].
Listing 2 - Error message when using unsupported font size.

If you need another font size for the article class you can use the extarticle class which allows to specify 8pt, 9pt, 10pt, 11pt, 12pt, 14pt, 17pt or 20pt.

2. Configuring the Latex Font for Parts of the Document

If you want to change the font size of specific parts of the document you can use {\Huge the big text} for for making the text "the big text" very big. See listing 1 for a example and figure 2 for the resulting PDF. Instead \Huge you also can use \huge with a small "h", \LARGE, \Large, \large, \normalsize, \small, \footnotesize, \scriptsize, or \tiny.

\documentclass[10pt]{article}

\begin{document}
Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy
eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam
voluptua. {\Huge At vero eos et accusam et justo duo dolores et ea rebum.}

At vero eos et accusam et justo duo dolores et ea rebum. Stet clita
kasd gubergren, {\tiny no sea takimata sanctus est Lorem ipsum dolor sit amet.}
\end{document}
Listing 3 - Only changing the font size for certain parts of the document.
Comparing the LaTeX generated document with 10 vs 12 pt
Figure 2 - The resulting PDF with only parts of a paragraph changed the font size

If you want to change the font size of large part of the document you can use \begin{small} and \end{small} to encapsulate the part which should be smaller (see listing 3).

\documentclass[10pt]{article}

\begin{document}
Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy
eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam
voluptua. At vero eos et accusam et justo duo dolores et ea rebum.

\begin{small}
At vero eos et accusam et justo duo dolores et ea rebum. Stet clita
kasd gubergren, no sea takimata sanctus est Lorem ipsum dolor sit amet.
\end{small}

\end{document}
Listing 4 - Only changing the font size for certain parts of the document.

The actual size in points depends on the global font size configured in the document class. Table 1 gives an overview what font size will result using a specific command in context with a specific document class configuration.

  Font Size in Document Class  
10pt 11pt 12pt
\tiny 5pt 6pt 6pt
\scriptsize 7pt 8pt 8pt
\footnotesize 8pt 9pt 10pt
\small 9pt 10pt 11pt
\normalsize 10pt 11pt 12pt
\large 12pt 12pt 14pt
\Large 14pt 14pt 17pt
\LARGE 17pt 17pt 20pt
\huge 20pt 20pt 25pt
\Huge 25pt 25pt 25pt
Table 1 - font sizes based on the font size in the document class.