Hallow Dear,
Let me answer your queries one by one:
1. Unless there is penile erection, the penis cannot enter the vagina. So penile erection is a must. If you are getting pain while he is inserting, follow some tips:
a. Do not let him in till you are completely wet. Relax your vagina while he is entering. Breathing by open mouth will help you at this juncture.
b. Use lubrication. Do not use oil based lubrication as they are harmful to women's genital organs. Use only water based lubricants. Vaginal jellies are good for the purpose.
c. An attempt to insert non-erected penis is always uncomfortable and painful for a woman.
2. Whether he is on the top or you, should not make any problem in insertion. Apply some lubricant to his penis and your vagina, then put the
glans of penis on your vaginal outlet and sit on it. Rest things will happen reflexly after that.
I am sure this will solve your problems. For any more information or guidance, you may ask me Direct question.
Dr. Nishikant Shrotri