Search lets you find files and metadata across your filesystem or in a specific stack. It is accessible anywhere within Finder top bar and using the keyboard shortcut /.
Search is in the header bar in the Finder.
Search can also be accessed within the Action Bar by tab-ing into Finder and doing a search.
Results will appear in the dropdown and you can click into them to go directly to the stack or file. If you want to search deeper, you can hit enter and go into the search page, where you can filter by searching for stacks, files or metadata.
Github search bar
Github advanced search page including filtering