Traditionally this was solved by using tables. There are more advanced solutions using DIVs and CSS, but tables are probably still the easiest way for a beginner.
Here's a very basic example of how it might look:
<table border="0" width="100%"><tr>
<td width="20%">
Navigation stuff goes here.
</td>
<td width="80%">
All the rest of the stuff goes here.
</td>
</tr></table>