Cascading drop downs let you pick fields to narrow down entries from another table and insert those fields into the current table.  This works well for picking make and model for cars or an item that is sold by a company.

1. In the designer click on the Cascading Dropdowns button in the toolbar
2. Drag over the control 'Cascade from [table name]' that is the table you want to select from
3. A window will allow you to select the fields from the source table and pick what fields to put them in on the current table

If you need to re-open the cascade editor please click on the "..." ellipse button next the the CascadingField property in the lower left side

The cascade editor allows you to select the fields to add onto the cascading control. The list on the left side is the frilds from the source table. The fields on the fight are the destination fields in the current custom table. To add fields follow these steps:

1. Select a field from the source table 
2. Click on the ADD-> button
3. From the popup form select the destination field and click OK

See also