Put the cursor on the function whose definition you want to open. Right-click and select "Open <name of function>". There's a keyboard shortcut for this, in the Windows default set of keyboard shortcuts it's Ctrl-D, but I'm not sure what it is on the Emacs or Macintosh default sets of keyboard shortcuts. The context menu should list the appropriate shortcut.
If you want to jump to a specific section or subfunction in a file, the Navigate section on the Editor tab in the Toolstrip has tools that will allow you to do this or set bookmarks (so you can easily jump between a local helper function and the place where it is called, to mention one way I've used bookmarks.)
