What is FTP?
FTP stands for File Transfer Protocol, and it's the standard manner by which files are transferred from your PC ("client") to a hosting server. 
FTP also allows you an easy way to change things such as permissions on your files, to create new directories on your site, to rename or delete a file...

I just uploaded something and I can't see it! What's going on??
Once in a while, when you've just uploaded a file via FTP, it won't show up on the list of files in your FTP client. Try refreshing. 
In Filezilla: press F5
In CuteFTP: Either press F5 or right click anywhere in the window you'd like to refresh and choose 'refresh' from the menu. 
In WS_FTP: Select 'refresh' from the group of buttons on the right hand side of the screen.

What software do I need to use FTP?
In order to use FTP, you'll need an FTP client.

There're many different FTP client, both free and licenced.
The most popular clients are:

• FileZilla (free, open source, available for Windows) 
• CuteFTP (paid, available for Windows or Mac OS X)
• WS_FTP LE (free, available for Windows)

We recommend to use only FTP clients downloaded from the official site!

Can I use FTP before my domain has propagated? 

Yes, it's possible. To do this you must specify in your FTP client to connect not to the hostname of your domain (that's to say, mydomain.com ) but to the IP or the hostname of the hosting server (other login data, username and password do not change
Once the domain has propagated you can change back your client to use the hostname of your domain