A custom form works in the same way as a built-in dialog box like Task Information. In a view like the Gantt Chart or Resource Sheet, you select a row in the table. Then, you open the custom form, and fill in or edit values in the boxes. Project saves the values to the selected task or resource when you click OK. The box on Creating a Form describes ways to simplify opening custom forms.
Figure 24-7. If you didn't create a lookup table, you must type a value and hope for the best. If the value doesn't match the code mask, an error message with the correct format appears. With a lookup table, click the down arrow in the cell, and then choose the value you want.
If you're comfortable editing in a view table, you may not need custom forms. Dragging over cells to copy values is surprisingly fast. You can supercharge table editing by arranging the columns you fill in side by side or by creating a custom table with just the columns you want (Changing Table Contents).