For comfort in entering anally, it works to be really turned on before anal entry. Deep kissing, squeezing nipples, rubbing the vulva and having vaginal sex for a few minutes first really helps to relax the anal muscles. Using lots of lubricant, the penis can push slowly, and if there is any tightness at all, withdraw and wait until the woman feels ready to do it again. The second time again entering slowly will be more relaxed and ready. If the woman rubs her vulva hard as entry happens it will more likely be pleasurable . If not, withdraw and try again when ready. Certainly it helps to have a caring partner who you can trust to be gentle. Once you are warmed up you can go pretty hard and it’s likely to give you a really great orgasm, more than you get vaginally.
The anal sphincter acts as a bit of a gatekeeper for the rectum. For anal sex, however, it’s important that this muscle relaxes. Not only does it make the experience more pleasurable, it reduces the risk of tearing or discomfort. Relaxation involves patience, both at the time you’re attempting penetration, and as you become more accustomed to anal sex.