To upload files into your website using FTP you need both to create an FTP account (on your cPanel), and to download an FTP application.
Now open your FTP application, enter your FTP configuration settings on the software, and connect. You should upload all your files to the public_html directory. This is where your main website will appear to the public. Below we use CoreFTP as an example, but you may use any FTP applications, their functionalities are all pretty much the same.
Using FTP you can quickly upload files when building or modifying your website. You can also download files from your website to a folder in your PC as backup just in case.
If the DNS propagation is yet to compete it would be better to use the
File Manager as explained on the next page.