This is a science fiction novel by David Gerrold. It was Gerrold's first novel, originally published in 1973. He'd already made a name for himself writing "The Trouble with Tribbles" for the original Star Trek television series1, so the next thing he did was he wrote a novel.
Gerrold always wanted to be Robert Heinlein when he grew up. Heinlein did a take on this idea in "By His Bootstraps" (1941), and another in ""All You Zombies"" (1959) (yes, just like that, in quotation marks). The former is a better story; the latter is closer to what Gerrold did. It's not an inferior story because of anything it has in common with Gerrold; the problem is that it's got that Cutesy Heinlein Sex Thing going on, which marred so much of his later work. Well, never mind that. Just read those too, so you can see this material handled by a much better writer (the plot is a machine. Heinlein wrote two simple implementations of it, while Gerrold did a very elaborate one).
The novel works like this: Our "protagonist" is named Dan. Dan doesn't have much family, just his rich old Uncle Jim. Soon enough, Uncle Jim dies, leaving Dan a funny belt. The belt is a Time Machine (oooh! ahhh!). Dan uses the time machine in the usual predictable ways. He makes money in the stock market, betting at race tracks, etc. Gerrold has the decency not to bore us with too much detail on all that. Dan's experiences getting used to the whole thing are a good read at first, but he keeps going back in time to advise himself, so we get the same scene twice, both times through the eyes of the same character. The second time he's driving the car instead of riding in the passenger seat, for example. This goes on for a while, and it gets old. The only really affecting part is where we're shown a room full of old versions of Dan, just... waiting. They're waiting in that room because that's the room where they know (from past experience) that the very oldest version of Dan will have a heart attack and die. Naturally, they'll end up there too.
The next thing Dan does is fuck himself, so to speak, and he spends most of the novel doing that. You see, if you've got a time machine and you're bisexual, you can make a hot date with yourself in the middle of last week. In fact, if you've got the money, you can throw an endless party featuring dozens of yourself. This is what Dan does. Wish fulfillment is a bore to read about, unless it's a wish to be a Mickey Spillane character.
In the meantime, the author has his eye on the plot, so he has Dan meet a woman named Diane and fall in love. They're too much alike, so they don't get along too well, but they do have a child. This is where it gets fuzzy: Through some mysterious Super Technology Hand Wave, Dan induces the fetus to be male, while the woman induces it by different mumbo-jumbo to be female. Both seem to be born. This looks more like an alternate universe thing than a single universe with a single character "folding" (get it?) himself. Dragging alternate universes into it offends against the minimalism of the work: One character, one idea, etc. etc. (Aristotle, anyone?) In general, it's just bad craftsmanship for science fiction stories to up and drag a second Big Idea into the plot three quarters of the way through. It looks like the author's waving a wand to get himself out of a tight spot -- and this is a very tight spot indeed, because the truth is that she's Dan, too, and so is (are?) the kid (kids?). The whole story breaks if they don't generate both a male Dan and a female Dan. Heinlein found a better way to fudge it, but that gimmick was too tied into the detail of Heinlein's story for Gerrold to steal it.2
So that's the deal: It's a closed loop. Dan's Uncle Jim is, of course, Dan. Diane is Dan with two X chromosomes. They become their own parents. Where did the "time belt" come from? It came from Uncle Jim, but of course that's not an answer! For that matter, where did Dan come from? None of it came from anywhere; it all came from itself. It's very weird, and pretty cool. Note that this "hole" doesn't need to be patched: It's not a hole in the plot, it's the punchline. The story's irrational, and that's the story. Duh, yeah, whatever, but it's cute.
It could have been a lot better if it'd been more story and less high concept. Gerrold was very young, but that's neither here nor there: He puts one character under a microscope from every conceivable angle for a hundred and sixty-five pages, but at the end of it all Dan is a cipher. There's no sense of knowing this person, nor even that there's very much there to know. There may be a "point" to that, but my guess is that the author wasn't much of a writer yet when he wrote it: There are few memorable scenes and no memorable images. The whole thing slides past, leaving nothing but the idea of the plot. It's a good idea for a plot, but it can be expressed in less than 165 pages: Heinlein did it in fourteen pages, with more memorable stuff than in this whole novel. If there's nothing to give a damn about in those extra 151 pages, there's no good reason to have written them, much less to read them.
I'll grant that it's hard to write a book with only one character. I'll also congratulate Mr. Gerrold for having had the nerve to try it, and (faint praise dept.) for having done a better job than Samuel Beckett usually did. At the end of the day, you should read this thing. It's one of those not-so-great SF books that you really have to have read if you want to have some grasp of what the field is about. After you've slogged through, you can treat yourself to some fine old Robert Silverberg (Downward to the Earth is a good choice) to get that bland taste out of your mouth.
1 He got that idea from Heinlein's novel The Rolling Stones (1952). If I recall correctly, he's into the same cult Heinlein was into -- Scientology or libertarianism, or something like that. One of those ranting-fringe-nut things. Maybe it was reflexology?
2 Heinlein's gimmick is the one in ""All You Zombies"". I can't think of another one myself, but then again -- isn't this what we pay SF writers to do? You know, make shit up?