Excitement is a nice feeling you get in your body when something sexual happens. It often starts as a tingling sensation in your genitals. Many things can make you sexually excited: a kiss, a sexual touch, a remark, a fantasy or someone who catches your eye. All kind of changes take place when you get excited:
With girls the vagina gets wet, within 10-30 seconds after the first titillation. At first you may not notice this. But when the arousal increases, the fluid may run between the inner lips. At the same time the inner and outer lips swell, the vagina lengthens and the clitoris increases in size. The nipples often get erect.
With guys blood streams into the penis, making it stiff. When excitement increases the testicles increase in diameter about 50% over their normal size and draw closer towards the body. The top of the penis often becomes wet with pre-come. The nipples can also become erect at a later stage.
During masturbation or lovemaking your excitement will increase. Your heart beats faster, the breathing rate increases and it becomes irregular. With 50-75% of the girls and 25% of the guys a sex flush arises.
After a while the increasing tension can come to a climax, which creates an intense pleasure.

The five stages of arousal.
Individual differences

When I’m very excited my glans turns purple. What’s wrong?
I was confused when I got excited during a physical exam.