C-s (isearch-forward) and C-r (isearch-backward) are two of the most useful Emacs keyboard shortcuts you’ll ever learn. To search forward interactively, type C-s (isearch-forward) and the first few characters of your search. Repeat C-s (isearch-forward) as necessary, or type in more characters to jump to the first instance that matches all those characters. Use these shortcuts to not only search your Org file, but also to quickly jump to sections. For example, I often search for headlines by typing C-s (isearch-forward) * start-of-my-headline. Org searches collapsed sections, so you don’t need to open everything before searching.

To search using Org’s outline structure, use C-c / r (org-sparse-tree, regexp), which will show only entries matching a regular expression. For more information about regular expressions, read the Emacs info manual entry on Regexps. Here are a few examples: