The act begins with Friar Lawrence speaking to Paris about the wedding. Later while they talk, Juliet enters while Paris was leaving. Once Paris left, Juliet ask Friar Lawrence to help her prevent the wedding, so he decides to give her a poison that doesn't kill her, but put her in a dead-like sleep. In the hopes that Romeo finds out about the plan to come get her from her family's tomb after the poisons effect wore off.
The next day, the Nurse goes to wake up Juliet for the wedding, but finds her "dead" (but not really). While lamenting about Juliet's death, Friar Lawrence tells Lord and Lady Capulet that Juliet is R.I.P. and requests that a funeral is prepared for her.
Hope this helps.