Enable Cloud sync to store all to-do's in cloud and sync to-do's with your multiple devices.
Follow these steps to setup cloud sync.
Open To-Do Prime app.
Tap on menu icon in top left corner.
Tap on Settings icon at the bottom of slide out pane.
Now Tap on Sync and then Cloud Sync.
Tap on Sign In and pick the account type that you want to use for syncing. Same Microsoft account must be used on all the devices to setup sync.
Once sign in is successful, sync setup is complete.
Go back to main page by pressing back button.
Perform sync operation.
To-do's are now syncing and will be stored in cloud.
Follow the same process on all other devices.