It's just a chronologically arranged encyclopedia of UESF and UFP Starfleet starships, in the style of Bill Gunston combat aircraft books, with a list of specs first, followed by a freeform article on the ship that describes the design, the reasons Starfleet wanted a ship like this, and possible associated pseudohistorical hijinks.
It contains all the canonical starship designs plus at least thrice as many ships from popular noncanon sources, primarily from RPGs (such as FASA or Star Fleet Battles), from computer games (Starfleet Command, Legacy, Starfleet Academy) and from classic books that turn unused sketches by the show's artists (Jeffries, Probert, Sternbach) into actual starships (Ships of the Star Fleet). It also adds ships mentioned or described in novels, and sometimes even in comics. The backstage "making of" books and tech manuals are also included.
It takes considerable liberties with the material to make it maximally consistent with modern canon. It tries to steer clear of introducing all-new, original ships, though, as the wider Trek universe is already chock full of designs. Also, if there exists a shape without a name (say, a study model or a background kitbash) and a name without a shape (a mention in a novel or sometimes even in onscreen dialogue), it tries to merge those two to keep things more compact.
Googling for "Hobbyist's Guide to the UFP Starfleet" turns up surprisingly many older versions in circulation, mostly at rather filthy upload or torrent sites...