Go to [https://lucid.app/](https://lucid.app/) and log in to your account.
Click the "Diagrams" tab at the top of the page.
Select the diagram you want to add a grid to.
Click the "View" tab at the top of the page.
Click the "Grid" button in the toolbar.
Select the type of grid you want to add from the drop-down menu.
Click the "Apply" button.