“hostname” for theme installation

Hello,

I’m new to wordpress and I successfully installed it and am now trying to play with themes.

When I choose a theme to install, it asks for a hostname. I tried the root directory such as:

http://www.mywebsitename/folderwherewordpressis

along with my ftp login and it did not seem to work. What exactly should one put in for the hostname?

Thanks!