When you first click to create a new dataset this is how the page will look.

Enter a name for your new dataset and select the Visualization Type that this dataset is meant for: either Table or Chart. For this example we're using Chart. Also select your dataset series. The choices are single and multi. Charts can be either single or multi but tables are purely single series. For this example we're selecting multiple series.

After you've selected a series some sample data in a spreadsheet will be displayed on the page as well as a way to preview this data in a chart.

Notice the row with 4 buttons, 2 with a green plus symbol and 2 with a red minus symbol. The two buttons on the right add/remove rows and the two buttons on the left add/remove columns. We're going to add a row.

The row was added and we manually populated the 2019, 40, 16, 13, 18 into this spreadsheet row.

Next we clicked green plus symbol button on the left side to add a new column and we populated it with Lexus, 22, 22, 22, 22.

After you're satisfied with the data you've entered into the spreadsheet you can click "Preview Population" to take a look at how your data looks populated in a chart.