Usage (Mac OS-X)

Type control+shift+p to call up the Command Palette

Type "install" and hit enter. Wait for the package list to appear.

Type "markdown preview", hit the arrow keys a couple times to select "Markdown Preview", and hit enter.

Reference:-

• http://plaintext-productivity.net/2-04-how-to-set-up-sublime-text-for-markdown-editing.html