How to scroll in a terminal using keyboard?

In "terminal" (not a graphic emulator like gterm), Shift+PageUp and Shift+PageDown work.

I use the default terminal in Ubuntu 14 (bash) and to scroll by page it is Shift + PageUp or Shift + PageDown to go up/down a whole page.

Ctrl + Shift + Up or Ctrl + Shift + Down to go up/down by line.

This depends on your terminal emulator, not the shell you are using. I personally use GNU Screen. From the description:

Screen is a full-screen window manager that multiplexes a physical terminal between several processes, typically interactive shells.

You can use C-a [ to enter scrollback mode. From here, you can scroll with the keyboard and even copy and paste. The mode can be exited from by using the Esc key.