How to do a case-sensitive search on Emacs?

You press M-c after you run search.

This will set the case-sensitive flag.

More generally, you can do: C-s C-h b to see all keybindings active during search, in isearch-mode-map.

In addition to M-c mentioned by alinsoar, entering a capital letter as part of your search string will cause the search to be case-sensitive.