Ever tie a string between two tin cans to make a "phone" when you were a kid? Whatever you say into one can comes out the other can with only that little string connecting the two.
That's what FTP is like.
FTP stands for File Transfer Protocol, which is a fancy way of saying it's a can-and-string phone, but for computer files instead of speech.
FTP is a protocol (an agreed upon way computers will act regarding a certain task).
Using FTP software, you can send a file from your computer (your "can") across the Internet (the "string") to another computer (the other "can") where a duplicated copy of the file will end up.
You can also get a copy of a file from another computer using FTP software.
You can also delete a file on another computer.
Or rename one.
Or create a folder.
In fact, with FTP software, you can basically do any type of file management on another computer that you could do on yours.
Now if you're thinking someone could use FTP software to get into your files and delete them or rename them or whatever, don't worry.
Unlike the can-and-string phone, not just anyone can grab the other end of the line and gain access to your end.
You need a username and password, and you need to know where the other computer is on the Internet.
In other words, you have to have some inside info before you can use FTP to hook up with another computer.
Web developers use FTP a lot, because they create webpages on their personal computers, but then need a way to get them onto the server where others can access them on the Internet.
When the webpage file is ready, the web developer will send the file to the server through FTP.
And that's why FTP is like a can-and-string phone.