The way my wife and I started was when we went to birthing class. As part of preparing the nurse had us practice at home. Basically, my wife on her back legs spread (which sometimes got tiring) or on her knees with her breast to the floor. Then I would finger her with a finger from each hand sliding in and out but then also slowly pulling apart once she felt good with 2 and loosening up I would add a finger, get her loose more then another so now using two fingers from each hand. Now I could also stretch each of the four fingers apart stretching her as well as she already had four fingers inside. After a few weeks I was able to pretty easily get four fingers inside her but at the same time she still felt tight on my cock (before each stretching 😀
. PS…lube as needed!