Saving and building is done on the left side of the Editor.
"Save" only saves the actors data back its .smubin files and ecodes them back with yaz0. "Save & Build" does the same, but also packs everything back together to a complete .pack file. "Open Build Folder" opens the place where the created .pack file is located.
Note: Because it is very likely that the shrine may crash, everytime you save&build, a backup is created.
These file are located besides the "build" directory in a folder named "backup".
Using the Mod
There is currently no clever way to apply the changes to the ROM files.
You need to manually copy&paste the .pack file into the "/content/Pack/" directory.
There is however a Mod-Manager planned, but that's in the far far future... Note: Please always make backups of the original files!