He is making arrangements for his wedding to Juliet, just as Romeo did in Act 2.
she says truthful things to hom that he understands
Paris is there, arranging his wedding to Juliet.
When Juliet arrives at Friar Laurence's cell, it is Paris who is speaking with the Friar. Paris is there to discuss marrying Juliet, but Friar Laurence is aware of her secret marriage to Romeo. This sets up the conflict that will lead to the tragic events of the play.
Well Juliet sends the nurse to go talk to Romeo to find about marriage, and Romeo tells the nurse to tell Juliet to go to Friar Lawrences' cell to be married
The first time when she arrives at his cell, Romeo is there ready to get married to her. The second time Paris is there, making arrangements to get married to her. There's a kind of parallelism there.
Killing himself
Juliet goes to Friar Laurence's cell in the play twice. The first is to marry Romeo and the second is after she learns of her prospective marriage to the County Paris. The latter time she seeks his help to stop the marriage from happening so that she may remain faithful to her Romeo and bee reunited with him.
Juliet meets Friar Lawrence at his cell, where they form a plan to fake her death using a potion that will make her appear lifeless. She hopes to avoid marrying Paris and reunite with Romeo.
Friar's Cell
Juliet goes to Friar Lawrence's cell in the hope that he will be able to devise a plan for her that will prevent her marriage to County Paris. The Friar gives Juliet a potion which will make her sleep, this is all part of the plan to reunite the two lovers.
Well, honey, Friar Laurence is in a cell because he messed with the wrong crowd. He got himself mixed up in Romeo and Juliet's drama, trying to play matchmaker and botching it big time. Now he's stuck behind bars, probably regretting ever getting involved in the first place.
He gives her the Sleeping Potion to simulate death, so that she can avoid marrying Paris and committing bigamy.