Swift is using Gulliver's voyages to satirize various aspects of English society. Gulliver's various conflicts in the lands he visits allow Swift to discuss a number of problems he sees with English society and the way England is governed.
When Gulliver washes ashore on Lilliput, for example, he soon observes that the Emperor of Lilliput chooses his ministers not on the basis of their ability to govern but on their ability to walk a tightrope. This is Swift's thinly-veiled criticism of how George I, the King of England, chooses his ministers--in this case, not on their ability to walk a tightrope but on their connections within the court and whether or not they will make decisions based on what King George wants them to do rather than on what is right for the English. In another instance, Swift, through Gulliver, criticizes the religious animosity within English society by telling us about the hatred between those Lillitputians who open their eggs from the small end or the large end first. The point is, of course, that it doesn't matter what end one opens an egg, but Swift is pointing out how ridiculous some controversies are.
Again, in the third voyage, to the island of Laputa, Gulliver discovers a race of people who are so detached from reality that they require their servants to carry inflated bladders and hit them in order to remind them bring them back from highly speculative thought to real-world concerns. Gulliver tells us, for example, that some of these people are actually trying to build a house from the top down, a physical impossibility, but symptomatic of how removed from everyday reality these people are. Swift is satirizing the over-abundance of genuine "projectors" in England who were...
constantly coming up with outlandish and unworkable ways to cure society's problems.
When Gulliver lands in the land of the Houyhnhnms, he discovers a race of horses who are perfectly rational, unemotional, logical beings, and the uncivilized brutes of this society, the Yahoos, are human beings. During this experience, Gulliver actually loses his own identity and considers himself a kind of Houyhnhnm rather than a human being, and when he returns to England, he can barely stand being around people, preferring horses for company. Swift is satirizing anyone who chooses a philosophy over reality.
In the end, Swift has managed--through the framework of a child's fairy tale--to point out many problems in English society that need correction, and he has accomplished this without pointing overtly to specific people within English society.