Rose Church is very famous in Elden Ring for its unique appearance, and it is also one of the important parts of completing the White Mask Varré quest line. You can find a lot of interesting background stories and precious Elden Ring Items here.
When you enter, you can go to Liunia Highway South Site of Grace first, then go north along the road until you reach Liurnia Highway North, and then continue to the Gate Town Site of Grace.
You can find a lake here, jump in and continue walking northeast until you reach the outer wall of Raya Lucaria and stop. Then you continue to go left and you can reach Rose Church.
After you talk to Varré here you can continue the quest, you have to keep talking to the NPCs and fulfill their requests and finally you can complete the quest. You can get a Pureblood Knight’s Medal, which you can use to get Varré’s bouquet.
Of course, to complete the task line requires a very strong strength, if your strength is not enough, you may die on the way. You can buy Elden Ring Runes to strengthen your class, I recommend you a website - IGGM. This website is very professional and cheap, I believe it will meet all your requirements.