As you already know there are some basic settings in a grid configuration. Here you can find details about these settings. The configuration is applicable for both Grid and View fields.
Basically grid settings are divided into 3 blocks:
Columns: here you can add and configure columns. All of the existing columns will be displayed here.
Below you can see the grid itself. It's possible to edit data directly from here or using the issue view.
Start editing data inside the grid by clicking 'pencil' button, then use use 'plus' button to add rows. Once you've finished, click 'tick' button to save changes.