Drag from the edge of a node to anywhere on the canvas. (or focus a node and press "C")
Drag the handle on the left-hand side of a node. (or focus a node, press "Spacebar" and use the arrow keys)
Select a node by clicking/focusing the drag handle and then press "Backspace" to delete.
Hover over the node and then click the color palette icon in the top right to choose a new random color.
To export the mindmap as an image, click the image icon in the bottom left of the mindmap.