Tables are a great way to quickly create and communicate information. To create a table:
Add a shape to your canvas (if you don't have one already) and select it.
Touch and hold your selection, then release. Tap more... in the context menu that appears; then, tap make table.
OmniGraffle will automatically group and arrange your shapes to create a table. The table will have one column and as many rows as shapes in your original selection. For example, if you had three shapes selected, you will end up with one column and three rows.
To add more rows and columns:
Tap the table to select it.
Drag the handle on the right to add more columns. Use the handle on the bottom to add more rows. Any additional rows will match the last shape of the original table. So, if Row 1 was a circle and Row 2 was a square, any new rows will be squares.
If you prefer to use a menu, touch and hold your table, then release. Tap more... in the context menu that appears; then, tap add column or add row.
To add labels: select an individual shape in the table, then double-tap to show the keyboard.