When you first open the design canvas, the row tab will be opened. From this tab, you will be able to drag rows onto the canvas, as well as add in nested rows and change the amount of columns in each row.
The Row Tab
Row: For you to be able to place tiles onto the page, you will need to place rows onto the page. In order to do this, you will need to grab the row icon and drag it onto the canvas. This will create a new row.
Nested Row: If you would like to nest a row inside an already existing row, you will be able to do this using the nested row option. To do this, grab the nested row icon and drag it onto the desired row column that you would like to put the nested row into. This will create a new nested row on the page.
Column buttons: A set of buttons are under each of the responsive size settings. These allow you to choose the number and spacing of the columns for each individual row. This lets you select how many tiles you want to place in a particular row as well as what it will look like on smaller devices.