Your first web site page must be named index.html (or in some cases index.htm) , so click into its name in the right side of the FTP browser and rename it.
If that isn't enough for the page contents to show up at your website, then you probably need to put the file into a special place - usually there is a folder named www or web, for example. I can't tell you where exactly to put it because it varies from one web site to another, but your web hosting provider should be able to answer this as well as any other questions you might have relating to the website.
