File links can contain additional information to make Emacs jump to a particular location in the file when following a link. This can be a line number or a search option after a double colon.
Here is the syntax of the different ways to attach a search to a file link, together with an explanation:
[[file:~/code/main.c::255]] Find line 255 [[file:~/xx.org::My Target]] Find ‘<<My Target>>’ [[file:~/xx.org::#my-custom-id]] Find entry with custom id
Chapter 4 of the manual