How do I physically upload files to my server?

1. Best practice is to use and ftp program, called an "FTP Client"

FTP = File Transfer Protocol
FTP Client = Generally user-friendly program you install on your PC that enables you to connect to a webserver and upload or download files from PC to server and vice-versa.

There are many good free and paid FTP clients from which to choose, you can try WS-FTP from www.ipswitch.com or surely many others will have suggestions as well.

2. Another way is to use the "File Manager" program in your online web management panel. Usually, when you pay for webspace, you gain access to a web control panel for your space at the server. Also usually, the web control panel will have a built-in file manager somewhere that will enable you to transfer files to and from your PC and move them around on the server.

Most Importantly While it is understood that you can't install CubeCart without some knowledge of how to do this, fact is, this is beyond the scope of CubeCart forum. For specific help about moving files up and down from your particular web server (which will apply to having any type of website, not just CubeCart), please contact your web host.