Using public transportation in Munich:

MVV site with tariff zones description and PDF map download:

http://www.mvv-muenchen.de/en/tickets-fares/tariff-maps/index.html

The MUC Airport is in the red zone, called Außenraum and the Messestadt is in the green zone called Innenraum.

The only one option that covers both zones is the Entire Network Ticket aka Gesamtnetz: http://www.mvv-muenchen.de/fileadmin/media/Dateien/3_Tickets_Preise/dokumente/TARIFPLAN_2016-Gesamtnetz.pdf

Messe München indications:

http://www.messe-muenchen.de/en/meta/anreise/anreise_mit_oeffentlichen_verkehrsmitteln/anreise_mit_oeffentlichen_verkehrsmitteln.php

MVV Tickets prices:

http://www.mvv-muenchen.de/en/tickets-fares/index.html

MVV Ticket Shop: (for diy printed ticket)

https://ticketshop.mvv-muenchen.de/index.php/tickets

MVV App for mobile ticket and planning:

http://www.mvv-muenchen.de/en/journey-planner/mobile-services/mvv-app/index.html