Why can't i see preference option in my finder?? It is only showing favourites and tags?

What do you see when you open Finder and the click on Finder in upper left? You should see:

About Finder

Preferences

Empty Trash

.....

Also what if you use the key shortcuts of Command + comma?

If you are referring to System Preferences, you can create a shortcut in the Finder Sidebar or you can click System Preferences in the Dock or you can use Spotlight (Command + Spacebar) and type "System Preferences."