Nested Grids – as the name suggests is a grid-within-a-grid (or rather, Grid-ception!). Nested Grids will let you expand a sub-grid entry to look at another grid of the expanded record. This depends on how you configure it.

Be aware, Nested Grids work with Editable Grids and only for Tablet, Phones and Unified Interface. This is not available for the classic Web UI.

Configuring Nested Editable Grid

Here’s my entity structure – I have Account, having multiple Contacts and each Contact, having Opportunities under them. Like in the below diagram –

Now, I have a Contact grid on my Account form (just like we usually do).

1. I now will have to choose the grid to be a Editable Grid Control as follows. Also, click on the Nested grid view control as pointed
   
2. On clicking the Nested grid view pencil, the next dialog box will let you select what entity you want the Nested Grid to be for. Note that this is with respect to the Contact entity and not the Account entity. For this example, I chose Opportunities.
   
3. On selecting the entity, I have to make sure my View is also correctly set to show the records
   
4. Now, my dataset will populate from the selected Entity and View. next we will need to select what should be bound as a key. Going back to the Nested grid parent ID pencil this time
   
5. Select what should be the field to bind the data. In this case, I want to show the one that is related to the Contact expanded.
   
6. Now, click OK for everything and your configuration should look like below.
   Finally save and Publish all customization.
   

Using Nested Editable Grid

Now, if you look at the Contact grid on the Account form. You’ll see an arrow on each record which indicates that it can be expanded.

And when you click on it, you’ll see the Nested Grid for Opportunities we configured in the section above

And yes, Opportunity too is editable in-line!

Hope this helps!!