In VIP the meanings of some keys are entirely different from Vi. These key bindings are done deliberately in the hope that editing under Emacs will become easier. It is however possible to rebind these keys to functions which behave similarly as in Vi. See Customizing Key Bindings, for details.
In Vi, C-g is used to get information about the file associated to the current buffer. Here, g will do that, and C-g is used to abort a command (this is for compatibility with emacs mode.)
Now these keys will scroll up and down the text of current window. Convenient for viewing the text.
They are used to switch to a specified buffer. Useful for switching to already existing buffer since buffer name completion is provided. Also a default buffer will be given as part of the prompt, to which you can switch by just typing RET key. s is used to select buffer in the current window, while S selects buffer in another window.
These keys will exit from vi mode and return to emacs mode temporarily. If you type C (X), Emacs will be in emacs mode and will believe that you have typed C-c (C-x) in emacs mode. Moreover, if the following character you type is an upper-case letter, then Emacs will believe that you have typed the corresponding control character. You will be in vi mode again after the command is executed. For example, typing X S in vi mode is the same as typing C-x C-s in emacs mode. You get the same effect by typing C-x C-s in vi mode, but the idea here is that you can execute useful Emacs commands without typing control characters. For example, if you hit X (or C-x) followed by 2, then the current window will be split into 2 and you will be in vi mode again.
In addition to these, ctl-x-map is slightly modified:
This is equivalent to C-x 1 C-x 2 (1 + 2 = 3).