Do you mean a web page you are designing or one someone else has put on the web ?
Because people have all sorts of screen sizes, and therefore browser sizes, it is important to make sure any web pages fit an 800x600 screen, and a 1024x768 screen and so on.
People used to put text in tables, and set the table width to be 100% ot 95% or whatever. Then as the browser page got smaller or larger the table would get larger or smaller to fit.
If the text is in tables, but it is set to a certain number of pixels, rather than a percent, that could be the problem. Maybe the table width is set at 800 pixels or more.
But nowadays the world has moved on and text should not be laid out with tables but with cascading style sheets (CSS).
CSS is too big a subject to cover here so look for CSS tutorials on the web.
Here is a web site that uses CSS to show you how layout can be controlled.
It does not teach you CSS but shows you how CSS can easily change the look and feel of a site. Select the different options on the right to change the look and feel.
Also notice how the text contracts and expands as the browser window gets larger and smaller.
This is all done with CSS
http://www.csszengarden.com/