A dry hump is rubbing your bodies together for sexually stimulation while you are dressed. So there is no direct genital-to-genital contact. It’s also called ‘clothed intercourse’ or ‘outercourse.’
You make the same movements: your bodies close together, genitals touching, while moving up and down. You can also use a circular motion.
For it to work the girl’s crotch must be moving against the penis (which should point upwards).
Sometimes it takes some effort to find a position that is satisfactory for both, the penis and clitoris/ lips being stimulated at the same time by moving the hips. But when you find the right technique you might be able to come.

Can I get pregnant from a dry lapdance?