Watch this video summary from Cliff's Notes, and this playful explanation from Schmoop... it'll make it all make sense.
And here's a prose summary from No Sweat Shakespeare. Enjoy.
Synopsis of Julius Caesar, by William Shakespeare
The tribunes, Marullus and Flavius, break up a gathering of Roman citizens who seek to celebrate Julius Caesar’s triumphant return from war. The victory is marked by public games in which Caesar’s friend, Mark Antony, takes part. On his way to the arena Caesar is stopped by a stranger who warns that he should ‘Beware the Ides (15th) of March.’
Fellow senators Caius Cassius and Marcus Brutus are suspicious of Caesar’s reactions to the power he holds in the Republic. They fear he will accept offers to become Emperor. Cassius, a successful general himself, is jealous, while Brutus has a more balanced view of the political situation. Cassius, Casca, and their allies, visit Brutus at night to persuade him of their views, and they plan Caesar’s death. Brutus is troubled but will not confide in his devoted wife, Portia.
On the 15th March Caesar is urged not to go to the Senate by his wife, Calphurnia, who has had dreams that he will be murdered, and she fears the portents of the overnight storms. He is nevertheless persuaded by flattery to go and as petitioners surround him Caesar is stabbed and dies as Brutus gives the final blow. Against Cassius’s advice Mark Antony is allowed by Brutus to speak a funeral oration in the market place after Brutus has addressed the people of Rome to explain the conspirators’ reasons and their fears for Caesar’s ambition. Brutus calms the crowd but Antony’s speech stirs them to rioting and the conspirators are forced to flee from the city.
Brutus and Cassius gather an army in Northern Greece and prepare to fight the forces led by Mark Antony, who has joined with Caesar’s great-nephew, Octavius, and with Lepidus. Away from Rome, Brutus and Cassius are filled with doubts about the future and they quarrel bitterly over funds for their soldiers’ pay. They make up the argument and despite the misgivings of Cassius over the site they prepare to engage Antony’s army at Philippi. Brutus stoically receives news of his wife’s suicide in Rome, but he sees Caesar’s ghost as he rests, unable to sleep on the eve of the conflict.
In the battle the Republicans at first appear to be winning but when his messenger’s horse seems to be overtaken by the enemy Cassius fears the worst and gets his servant, Pindarus, to help him to a quick death. Brutus, finding Cassius’s body, commits suicide as the only honourable action left to him. Antony, triumphant on the battlefield, praises Brutus as ‘the noblest Roman of them all’, and orders a formal funeral before he and Octavius return to rule in Rome.
http://www.nosweatshakespeare.com/play-summary/julius-caesar/