What does ** mean in a path?

@ is for verbatim string, so that the string is treated as is. Especially useful for paths that have a \ which might be treated as escape characters ( like \n)

../.. is relative path, in this case, two levels up. .. represents parent of current directory and so on.

new DirectoryInfo(@"../..") means "a directory two levels above the current one".

The @ denotes a verbatim string literal.

.. is the container directory. So ../.. means "up" twice.
For example if your current directory is C:/projects/a/b/c then ../.. will be C:/projects/a