What's a quickfix window and how to use it?

I just found out how to use vimgrep command to search for a particular string in multiple files. I know that the search results are stored in quickfix

I use :cnext to go to the next matching pattern. But this is not a feasible option if there are hundreds of search results.

Can someone please explain how to use quickfix?

The quickfix list is a list of entries containing position, file, and message. It often used for searches like :vimgrep and :grep as well as finding errors via :make.

Here are a few quickfix list commands to get you up and running fast:

• Use :cnext and :cprev to move between your errors/matches.
• :cfirst and :clast to go to the first and last error/matches respectively.
• :copen to open up the quickfix list in a window (:cclose to close)
• :cwindow to open quickfix list window only if there are errors
• :cc to display the current error/match.
• May want to use better mappings for :cnext and friends. I suggest Tim Pope's unimpaired plugin

For more help see the following:

:h quickfix
:h :cnext
:h :cfirst
:h :cope
:h :cwindow
:h :cc