The second line maps all document names onto filenames in a particular directory.
The third line allows access to all documenst in that directory.
The fouth line disallows access to all other documents. (There won't be in any in this case because of the mapping, but its wise to put in for later).
The second line maps all document names starting with /tnote/ onto filenames in a particular where john maintains the technical notes. If someone else takes over the technical notes, we can change this. Here we are starting to distinguish between document names and file names. This can be carried much further if necessary, but one level of mapping is enough to allow for changes of administration of different areas.
The third line separately maps the seminar information into Jane's directory.
The third and forth line enable access to anything in John's "public" directory, and any .html file in Jane's "seminar" directory tree. Note here that the * maps to any sequence INCLUDING SLASHES so all files in any subdirectory of /u/jane/seminars will be enabled so long as they end in .html.
The bottom line will pick up for example any attempt to use the server to access non-html files in Jane's seminar directory.