SSH (Secure Shell) was developed as a secure alternative to Telnet or Putty.
Putty is a protocol allowing for command line access to a Unix, Linux or FreeBSD based remote computer. If you've ever used DOS, you'd be familiar with the black screen. Some of the DOS command set will also work . If you're asking what DOS is, then you're probably a lot younger than I.
DOS was Microsoft's Disk Operating System; the precursor to Windows.