Drag each box into a sensible place (or focus it with Tab and use the arrow keys). Then draw the flows between them: click Draw a flow, click the source box, then the target box.
Add a boundary and drag it to enclose everything inside your trust (e.g. your AWS account) — anything outside it, like the mobile app or the payment provider, is on the other side.
Link one or more controls to each threat. Names are generic, AWS, Azure and Kubernetes — pick whichever fits the case.
For each threat: likelihood × business impact, a decision, and the reason for it.