Juliet, believing Romeo to be dead after he kills her cousin Tybalt, drinks a potion given to her by Friar Laurence. This potion induces a death-like sleep, making her appear dead. Romeo, upon seeing her lifeless body, assumes that she is indeed gone and drinks a fatal poison.
The dramatic irony lies in the fact that Juliet is not truly dead, and if only Romeo knew this, he could have been saved. Friar Laurence, who concocted the potion, is also unaware of Romeo's impulsive act and arrives too late to prevent his death.
This scene amplifies the play's overarching themes of fate, miscommunication, and tragic consequences, highlighting the impact of misunderstandings and rash decisions on the characters' lives.