What is the first percy jackson book about?

It was Percy Jackson and the lighting theif. zeuses lighting bolt was stolen by luke to destroy the gods and Olympus. but Percy Jackson a half blood Annabeth and grover went on a quest to find the stolen weapon and return it back before Olympus falls. but before that Percy was the prime suspect and to clear his name he had to find the bolt and the theif before a certain time.

I know there's already an answer above but it doesn't really summarize the book and he/she made some typing mistakes so I guess if you don't mind I could try to improve the answer.

The first book of the Percy Jackson series is named "The Lightning Thief". It is the first book of the entire series and it was so spectacular that it earned itself a series as a sequel.

This book is about a boy named Perseus "Percy" Jackson, an ordinary 12-year-old boy with ADHD.
On the first day of summer, just after his sixth-grade year, Percy learnt that he was a half-blood, or more precisely, half-human half-god, with a battle against the minotaur. He woke up in Camp Half Blood after his fight and was slowly introduced to the world of Greek Mythology.
Now, in the Mount Olympus where the gods stayed, Zeus, the king of the gods, had his lightning bolt stolen from him. It was his symbol of power. And due to rough histories, he suspected Poseidon as the thief. Poseidon was too proud to deny, therefore claimed Percy as his son and gave him a mission to find Zeus' lightning bold and return it to him before the summer solstice which was a few days away. It was believed that Hades, the god of the Underworld, had stolen the bolt for he was the only one that had the power of invisibility.
Percy, Annabeth Chase (a daughter of Athena) and Grover Underwood (a satyr who was assigned to protect Percy) went on a quest together.
After a long journey of meeting Ares, the god of War, nearly losing their memory in the Casino in Las Vegas, they reached the Underworld. Their plan was to try to pursuade the lord of the Underworld to hand the bolt so he could return it to Zeus and prove his father innocent. But the tides turned. Hades accused Percy for theft due to Hades' missing helm of darkness and they had to escape Hades' wrath with the help of Persephone. It was later known that Ares was the thief.
Percy battled Ares at the beach and Percy wounded Ares, winning the helm of darkness and the bolt.
They quickly returned to Mount Olympus to return the stolen objects and to clarify that they were innocent, and Ares was the one that was guilty for theft.
The trio went back to CHB after the quest and Luke Castellan, a son of Hermes and a "friend" of Percy and Annabeth, confessed that he was responsible for the stolen items and he had been working with Kronos, the Titan of Time, to defeat the Olympians. The reasons were not clear (but will be explained thoroughly throughout the entire series). Luke left quickly, but not before leaving a deadly scorpion to sting Percy. Percy fell into unconsciousness again but was rescued by wood nymphs. They brought him to Chiron, the teacher in CHB, and successfully healed Percy. Percy then decided to go home and continue his "normal" life as a seventh grader.

This is long, but I hope it helped as it is more detailed.
Good luck!