Filter option determines which data records will be bound to a section
Spreadsheet and Table can be bound to Data, that means that Spreadsheet section can be connected to one data record, and Table section can be connected to multiple data records.
Examples of lookup formulas in Filter:
=LOOKUP(SYSUSER) - Data SYSUSER, no query
=LOOKUP(PRODUCT, id=123) - Data PRODUCT, get product with ID 123
=LOOKUP(PRODUCT, price > 100) - Data PRODUCT, get products with price greater than 100
If lookup formula on spreadsheet section returns more than one record - first one will be used.