How do you determine the amount of col...

You need to decide how you want the web page to appear. Most simple web pages have 2 or 3 colums to separate the content. If you are adding images, this may influence the width of a colum. e.g. if an image is 300px wide, then the column should be at least 300px wide. A web page may be set to a size suitable for viewing in browsers, the most common widths being between 600 and 925px. So if a web page is 600px wide, you would only get 2 columns of 300px width, or 3 columns of 200px width.