You can add a button element on the Design tab.

To add a button:

1. Open the editor on the Design tab.
2. Choose Buttons on the Elements panel 1
3. Click on the chosen button element (choose one by style, you can edit the call-to-action text and color later) or drag and drop it onto the canvas.

To edit the call-to-action text on the button double-click it on the canvas 2 and type the text you would like.

To adjust its style, choose the element on the canvas and make changes on the Editing panel 3.