Adding a Single PayPal Button
If you would like to create a single paypal button you can use the paypal payment button designer which is here: https://www.paypal.com/cgi-bin/webscr?cmd=_button-designer
Its quite a handy little feature if you want to enable people to pay from various pages within your website.
Once you have created your button you will be give some code, simply copy the code and add it in the source section of your webpage where you want it to appear. There are some instructions on adding code into your site here