After you gathered enough gear and resources, you should build an Ender portal. The map is meant to be played in Adventure mode, which means that it has limitations in terms of building stuff. Find the apartment in one of the skyscrapers with signs in it - that is the only place you're allowed to build a portal.
Credits: Jarno
How to install maps:
- Download .mcworld file below
- Open file using any file manager to import it into Minecraft PE
- Open Minecraft Pocket Edition and look for the map among your worlds