How to paste from clipboard into KiTTY SSH terminal window?

Right-click somewhere inside the terminal window.

I pasted "administrator" by right-clicking somewhere inside the terminal window. (The black area)

Copy and paste works similarly to the X Window System. You use the left mouse button to select text in the PuTTY window. The act of selection automatically copies the text to the clipboard: there is no need to press Ctrl-Ins or Ctrl-C or anything else. The only thing you need to do, to copy text to the clipboard, is to select it. To paste the clipboard contents into a PuTTY window, by default you click the right mouse button. You can also paste by pressing Shift-Ins.

see: http://www.chiark.greenend.org.uk/~sgtatham/putty/faq.html

To paste into a terminal window press Shift+Insert.