Here is a very comprehensive and accurate introduction to everything Mesoamerican calendar based, including the long count and the Tzolk'in (which is included as part of the long count). I got this off FAMSI.org which is an excellent resource for anything mesoamerica. You can consider basically everything on the website as being more or less already vetted and of quality content. They don't say who put this presentation together, but it looks like it was probably Mark Van Stone who is a well-known epigrapher and a reputable source.