I couldn't zoom web pages in Internet Explorer using ctrl ++ and ctrl --, Why?

Because Ctrl ++ and Ctrl -- are short cut keys of Firefox. Using which you can zoom in or zoom out a web page only if your browser is Firefox.

OK, How to zoom web pages in Internet Explorer?

You have 5 options

View -> Text size -> smallest

Or

View -> Text size -> smaller

Or

View -> Text size -> medium

Or

View -> Text size -> largest

Or

View -> Text size -> larger

Select either one to zoom in or zoom out. Is it enough Mr. Cool?