Google is your friend. You can easily find the FTP commands and their syntax via Google. FTP is not specific to the mainframe and generally the commands work across platforms. If you want the commands specific to the mainframe (such as SITE or LOCSITE), find the Communications Server bookshelf on IBM's web site and look them up in the User's Guide.
However, if you think you will be able to create a batch job on the mainframe and submit it to use FTP to connect to your desktop PC and transfer a file -- you are mistaken. FTP connects clients (the originating machine) to servers (the machine on the other side of the connection). A desktop PC almost never runs server software and hence cannot be accessed as a server via FTP. This means the batch FTP job on the mainframe cannot connect to your desktop.