Bismillah
Let's see if I can bridge this communication gap...
FHC- I think (correct me, ukhti if I am wrong) that muslimah is asking about the actual rites and rituals that are practiced.
Maybe explain the seven sacraments and how they came about, like why (presedence for sacrament), when (became cannon) , and how (what is done and who set the example for doing these actions specifically).
Just bc I have background in both, I am going to try to pre-empt an answer.
The Eucharist (or Communion) has its origins in the Last Supper (btw muslim account of it is interesting, FHC. Start at verse 111. http://www.usc.edu/dept/MSA/quran/005.qmt.html).
What Muslimah might then ask is from where did the specific actions and methods come? Like why is an altar used when Jesus used a table? Why do people kneel or stand at certain times? Who commanded this?
For muslims, each act of worship that we do has been specifically patterned after the Prophet. Muslims then have a difficult time understanding why Christians will do some of the acts of worship they do when Christ never did it himself, like the sign of the cross.
Insha'Allah this helped rather than hindered. I apologize if I have said anything incorrect or offensive.
Peace