The editor supports full undo and redo, so you can experiment without fear of breaking your setup.
Try a connection, change a node’s settings, rearrange the graph – if it isn’t what you wanted, undo it; redo brings it back. Because you can always step back, the editor is a safe place to try things rather than plan every move in advance.
Undo pairs naturally with the preview: make a change, preview the result for one record, and undo if it’s not right. Build by trying and checking, in small steps, with nothing to lose.
That completes the node editor. Next comes producing your output – the Export section, starting with what happens when you press Merge.