I can try, but you won't be able to understand it unless you have a vagina. There is no other body part to compare it with, which makes it very difficult to explain what it feels like to own one, let alone what it's like to have it penetrated by something.
A vagina isn't a gaping hole, but rather a very narrow, elastic space where the walls are collapsed when it is empty. Most of the nerve endings that come into play during intercourse aren’t actually inside the vagina. All women will feel the sensation of being stretched when penetrated, and we all feel pain if our partner is rushed or clumsy, but penetration alone only causes some of us to feel the kind of sexual pleasure that leads to orgasm.
Some women experience physical pleasure when the small area on the front wall of the vagina known as the G-spot is stimulated, but others do not feel it at all. If you happen to have a sensitive G-spot, the pressure that a properly operated penis can put on it might feel a little like having your clitoris or frenulum touched. Every thrust can bring intense, almost stabbing pleasure when he hits that spot. However, many women need simultaneous clitoral stimulation in order to have an orgasm during vaginal sex. The clitoris is extremely sensitive and can be a source of pleasure similar to the head of a penis.
Penetration in itself makes you feel the sensation of having your vagina stretched on the inside as well as physical pressure around it. It may or may not be painful depending on the circumstances, but once your body has adjusted to the penis, you feel filled – not full. You can feel your own wetness and the sensation of the penis moving inside you. Depending on his size and the position, it might feel like the penis is pushing on other organs inside you. When we had sex this morning, I ended up in kind of a pretzel shape, and it felt like I should have been able to see his penis pushing out against my stomach.
I can feel it when he ejaculates inside me, but that is another thing that differs depending on the woman – and sometimes her partner. The actual ejaculation feels like wet pressure hitting the inside of my vagina. The twitching of the penis kind of feels as though it is kicking inside me. My own orgasms feel like powerful spasms when my muscles rapidly contract. It can become painful when the muscles want to squeeze tighter than the penis inside me will allow, and it feels like my body is trying to squeeze him back out.