To add a widget to your report you proceed by clicking on Edit → New Widget → Widget Type.

For example to add NPS Trend widget go to NPS widget type → NPS Trend or type a widget name in Search Widgets field.

When clicking on the chosen widget you can see Preview Widget, go to Continue To Widget Settings to set it up.

The default size for each widget is different and can be adjusted depending on your report, as well as the other settings. 

When you are all set click Add Widget.