IMPORT - this is where you get your data from various data sources into your spreadsheet.
From the Home Screen, click Import. Select your data source, then click the button to go to the next page where you'll be asked to choose which properties (or 'columns') you want to import. Then, you can filter according to what kind of data you want.
Home Screen → Select Source → Select Table → Select Columns → Select Filter (optional) → Summarize (optional) → Import
Here's a video demonstrating how Import can be used:
Importing data from Notion:
From the Home Screen, click Import. Select Notion as your data source, then select the database you wish to import (you can choose from a list, or search for it). Note that you should have already connected to the correct workspace for the database you're looking for to show up.