The assignment is shown along the left of the grid in the row headers. In the Step Sequencer, rows correspond to either kit pieces, notes, or automation data.
In tracks view, Control-click in an empty part of the Tracks area of a Software Instrument or MIDI track, then choose Create Pattern Region.You can also create a region or cell that uses the Step Sequencer: Click the Editors button in the toolbar, then click Step Sequencer. You can use any software instrument with Step Sequencer. To get started with the Step Sequencer, create a Software Instrument or an External MIDI track in your project.