Part 1 is a set of 15 short stories. The introduction says they've never been published in a book format before. I believe this means that they were published in a science-fiction magazine before. This is a eclectic collection of short-stories. They range from letters to earth from mars, politics, bionic humans and, of course, robots.
Reading "Cal" made me understand what satire was. His short-story "Feghoot And The Courts" is one page. Around 500 words. But it shows so much wit and humor. Same with "Left to Right" which is two pages long. "Gold" is the longest of the stories. It presents challenges to a futuristic movie/play production company. The story goes into creative challenges for the director and a casting director. I say casting director since I do not know what to call the profession of the character Cathcart.
Part 2 seems like his preface to anthologies that he presented. The anthologies are collection of stories by other authors. He publishes these anthologies as presented by him. This helps the books sell and hence help the authors. This is a very noble effort. The author claims that this is to get rid of the guilt. The guilt of being among the Big Three science-fiction writers. In his mind, this perception somewhat thwarts works by newer authors. I don't buy it. He was a good person. He did it since he empathized with the newcomers and lesser known veterans.
Don't be fooled thinking of this as mere prefaces or skip this part. Asimov gives his thoughts on alien invasion in the context of human history. He does this with flying saucers, travelling at the speed of light etc. They all make for excellent reads.
Part 3 is his advice to science-fiction writers. This is an amazing collection of his thoughts on suspense, irony, satire and how to use them in stories. Reading this will make you want to write something. It may as well be a good introductory course on science-fiction writing for. Were he alive today, Isaac Asmiov could lead a massive open online course on this subject. He uses his own work as examples to explain these concepts. Part three gives you a better appreciation of science-fiction writing. Even if you don't write anything.