People tend to report that the two easiest positions for new intercourse are either the missionary position (where the person with the penis is on top), or a position where the person with the vulva is on top. The latter may be a little easier because that person, who is more likely to have issues with discomfort, can control how deeply a penis is going into a vagina and at what pace. When you begin vaginal entry, go slow. Start by just setting the tip of the penis against the vaginal opening. You can learn a thing or two here from an eastern tantric tradition: if you simply set the penis at the vaginal opening, and either of you gently put your weight on the other and press down slowly as you both relax, the vaginal opening and canal will open to entry more naturally.