Uncompressing files….
If a file is compressed, after you download it you will have to uncompress it to use or run it.
Uncompressing the file may produce another single larger file, or a whole folder full of files
From there you might have to run a “Setup” or “Install” program to actually install the software that you just FTPed
There is some danger of getting a computer virus when you FTP files as you need to be careful