FTP stands for File Transfer Protocol, while SFTP refers to Secure Shell (SSH) File Transfer Protocol. This gives you file transfers that are secured via SSH, which provides full access to shell accounts. A shell account is one that sits on a remote server.
FTP is different from SFTP in that it does not give users a secure channel for transferring files. Also, FTP makes use of two channels for transferring data, but SFTP only uses a single channel. The inbound connections that each protocol uses are different as well. FTP defaults to port 21, but SFTP allows inbound communication on port 22.
The manner in which data is transferred is also significantly different. SFTP uses a tunneling method to transfer data. With the benefit of additional security, FTP, which is less secure, uses direct transfer.
