Can someone explain how private dm works on nostr 
nostr:nevent1qqspluxmhqnv47y4hn9m7tc5jkdzznmfq28hcvx9dntfptk4232mzcqppemhxue69uhkummn9ekx7mp0qgsydnna6k2n0pxsd2teh8w2cwfdgwpdph2gptkyqnhppg7awlxgz8qrqsqqqqqptql42t