why can't i open a new page in safari when i have one already open but reduced in the dock bar

You can but Safari must be the active application. If you look up at the menubar to the right of the Apple menu you can see what program is currently 'on top' or 'active'. That's the program that is receiving keypresses and mouse clicks. If Safari is active then Command N or File> New Window should open a new browser window - it did on my computer just now.