men and women actually have more or less the same parts, but our genes determine if we emit male or female hormones in utero. For example, men and women both have sensitive oval shaped sacks, but in men the develop into testes and drop and in women they become ovaries.
Although it isn't a penis, a woman's clitoris is probably the best way to for a woman to understand what an erection feels like.
When you're in bed or just feeling hot have you ever really wanted your clitoris played with?
An erection is going to be similar to that feeling, but being larger and also connected to the urethra. The head of the penis is the most sensitive part, probably feeling most like a woman's clitoris. It can feel amazing if it's licked, I especially like that from side to side where the head meets the shaft.
The shaft is pretty special. It can embarrass a man, like some mentioned earlier, but it can also be a source of great pleasure, and perhaps ego or shame depending on its size. As far as a woman imagining it, maybe imagine the clitoris is sitting at the top of a tense and tight, good feeling balloon that is about to make you scream and explode with ecstasy. Wow. I got carried away there.
Full disclosure: I've got wood right now. Jk, anyways...
A lot of the penis is also buried underneath the body's surface (so even if you're small, it's bigger than you think). Those little swimmers have to travel a relatively long way, it's not a direct ball to tip transfer. The base of the penis goes underneath the pelvis and then wraps around underneath the balls and towards the anus (don't get carried away, not TO the anus, TOWARDS it). So in addition to all that's going on up on the surface, there's quite a bit of anatomy doing its thing down there. You can access this part of the dick by touching underneath the balls or down just a little further in the taint. This area to me feels like an area where pressure builds up and it's inflating the pleasure balloon up top, but it's also feels great. For me, when it touched it makes the shaft feel even more tense. This is where men and women are way different. You guys have a hole inside of you and we have a pleasure pole that been set inside of us (imagine base of tether ball pole)
A woman (or man, whatever) could reach back and place her hand here when in a variety of positions and it always feels good. Cup the balls and apply pressure on the base of the penis with your fingers. Dont over reach! (Unless that's your/his thing)