How do women have sex with women?

Mostly like everybody else.

Yes, there are certain differences given that there are two vaginas and no penis, but broadly speaking, things are not that different.

Women start by flirting. Then they kiss and caress each other. Next, as the sexual excitement mounts, they move to more intense foreplay. 

They might rub their bodies and genitals against each other (dry humping), mutually masturbate, perform oral sex on each other, play with sex toys to stimulate each other, or put on a dildo (a sex toy shaped like a penis) and penetrate each other.

Then, like everybody else, if they are in the mood, they might cuddle for a while and fall asleep.