Do you want to hear about an easy dry run? I've had a vaginal birth so it's probably easier for me anyway. I did the C-fold and just pushed it in and turned it a little, felt it pop open, and then it was great. I ended up trimming about half the stem. It was very comfortable. To break the seal I kind of held the stem and bore down a little, and I felt the seal break, and then I gently pulled it out. I checked my IUD strings and they hadn't moved. So now I guess I'll wait a few more weeks for my period to start! The only thing I want to be careful of is to not put it in too far because of the IUD. But I think I got it about right.
Thanks to everyone in this community for giving information about how to use these. I was really intimidated by the idea until I read what you've all said.