The Republic of Plato Plato's books on The Republic are a classic, however not very useful.
Plato himself was frustrated with Athens and with democracy due to the execution of his teacher Socrates. Socrates was charged with corrupting the youth in his school with notions that there was no evidence for Zeus and his Pantheon. The ancient Greeks were very religious and superstitious and they feared that to leave Socrates unpunished would be to offend the Gods.
But the Athenians gave Socrates every chance to escape punishment by exile. Socrates was simply stubborn and decided to stay. He should have left. There were plenty of islands in the Aegean where he could have resettled. Miletus is the classic example.
Anyway that is the background.
Plato wrote his Republic to mirror the Spartan government, only instead of being ruled by two kings Plato invents a philosopher-king. The idea is ludicrous.
As Machiavelli and Nietzsche later explained, government is the will to power and nothing less.
So Plato is pretty much a big waste of time. Even Aristotle would agree with me on this.
If you are starting from scratch I would recommend Aristotle.
However in universities they start with a survey of the history of Philosophy such as that written by Bertrand Russell. If you read Russell's book just beware of his prejudice in favor of atheism. Don't be deceived by it.