Although SFTP can be used as a replacement for FTP, it is not based on it. SFTP makes it possible to interactively transfer files between computers over a secure and encrypted channel. It is designed to be a replacement of tunneling FTP over an SSH connection, which can be a complicated thing.
A normal user can copy all files they like to their computer, where permissions allow. This means they can also cd to the file system root (/) and navigate throughout the entire system. If you would like to set up a SFTP server, limiting only specified users to a specific directory and its sub-directories, you will have to set up an SFTP server with Chroot.
If you have an SSHD listening, you can already access your computer through SFTP. By default the openSSH package comes with a SFTP client, which is will open a SFTP shell when invoked. eg:
In the default setup you will go to the home directory of this user on the remote host. If you type “help” you will get a list of commands which you can use. Some very basic bash commands are supported. (Like “ls” and “cd”).
More and more file manager support the SFTP protocol.
Doplhin supports SFTP