Dragging or resizing windows is quite easy - you just need to invoke Jump's left mouse drag gesture: Double tap on the screen but make sure you don't lift your finger after the second tap. Then, drag your finger across the screen to start the drag operation and lift your finger when you want to stop it. The gesture is very similar to the drag gesture used on a laptop's trackpad.
You can even use the same gesture inside the mouse circle for precise mouse dragging. Precise dragging is useful when you want to resize windows and need to drag just the window's edges. Note: The mouse pointer will not change to double headed arrows when you're pointing at the window's edges in Jump, but the drag gesture should still work if you're pointing at correct place.
To get used to the gesture we recommend trying to drag an icon on your desktop.
Recommended reading: Jump Desktop Control Gesture Guide