At various places in the app grids are used to snap your actions to the timeline.
For example in the sequence editor, when drawing a new note it will start at a grid position and end at a grid position so everything plays nicely in sync.
Grids are a collection of points in time that define the grid. The last point defines the grid's loop length.
Wherever grids are used you can click the grid display's option button to rename, add, edit or delete grids.
Upon editing a grid the grid editor appears where you can add, move or delete points in the grid.
As you see the grid editor itself also has a grid panel for in case you would like to use a grid while creating another grid.
By the default the grid editor's grid is set to No Grid.
You can open and save grids as preset files in your user library. These preset files have extension .MuTimeGrid.
You can also drag-drop an audio file or a sample onto the grid editor so to extract a grid from the (selected) audio's markers, eg. a sampled drum loop.
If the audio contains a selection only the selection is taken into account.