Simple Instructions:
Having defined a subcollection filter, use the "Assign Partitions" tab to build
indexes for it (or for a group of filters). Select the desired filter (or
filters) from the "Defined Subcollection Filters" list, enter a name for your partition in the "Partition Name" field, and click "Add Partition".
To remove a partition, select it from the list and click "Remove Partition".
To make a partition the default one, select it from the list and click "Set
Default".
To clear the default partition, click "Clear Default".