Hello,
If you want to use your PC to manage the library on a separate tablet (which means adding/editing songs, creating setlists, etc), you can use the free companion app:
https://www.zubersoft.com/mobilesheets/companion.php
This will let you connect to the device over WiFi and edit the library. If you instead want to be able to use MobileSheets normally on your PC, set up the library, then sync that library to your tablet, you can do that but it will require an extra purchase if your device is Android-based (one purchase is required per platform). If your tablet is running Windows 10, then you can use a single purchase through the Microsoft Store.
I'll assume you are going to use MobileSheets on your PC to set up the library and then sync it to your tablet. In that case, use Import->Local File to pull in new files which will create songs. On the import settings dialog, you can add the name of a setlist to add the new songs to. You can also edit the setlist on the setlists tab and add songs or reorder them if needed. Once your setlist has all of the songs in it, tap on the setlist on the Setlists tab, then tap Load All to view all of the songs in order.
To transfer your library to your tablet, tap the three dots at the top right corner of the library screen, then Sync Library->Sync to another device. Set the PC as the server, tablet as client, set sync type to "update client", then connect the tablet to the PC. You can do this anytime you need to sync new changes.
I would recommend reading the manual at
www.zubersoft.com/mobilesheets/manual.php. It covers all of this and more. Let me know if you have questions.
Mike