This means that you have a concept, develop the code to execute the concept, and then test the code to make sure that it all works properly. If you are developing a web site, drum this into your head. Enter the text, drop in the graphics, set the formatting, upload the file to the server, and your done. While the concept and coding may steps may receive sufficient focus. The testing step does not.
Testing is probably the most important step in developing a web site.
You should make sure that all the links work properly and point to the right location. You need to check that all your graphics appear as you want them to and that they can be found once the document is uploaded to a server. If possible, access the page from a number of web browsers to see that your site is adequately rendered by each browser. You should also make sure that your coding is sufficiently robust so that most browsers will not choke on it. Consider providing alternate coding for browsers that do not support graphics or newer html elements such as tables.