The same way anyone else does. Which is to say, any vast number of different ways.
Sex isn't just heterosexual intercourse. Sex is any number of combination of things people of all stripes do together to seek mutual sexual pleasure, and what those things or that combination are varies for everyone, even from day to say.
So, on a given day, Lesbian Couple A may want to engage in some mutual masturbation and some oral sex, while Lesbian Couple B may choose to engage in shared manual sex and genital massage mixed in with some role play, and Lesbian Couple C may decide to do some big-time snuggling paired with strap-on play.
There's really nothing heterosexual couples can do that lesbian couples cannot: even vaginal intercourse isn't exclusive to heterosexuals, when it's something lesbian women want, as it can be done either with hands or with sex toys. That said, intercourse usually isn't seen as "the" sex the way it can be in many male-female partnerships, given that a majority of women don't find intercourse all by itself that satisfying, but plenty of hetero couples have, by now, clued into the fact that intercourse shouldn't be the main thing on the menu, too. All the things most people think of as sex -- making out, frottage, manual sex, mutual masturbation, oral sex, vaginal intercourse, anal sex...you name it, lesbians can also do it.
Figuring out what it is exactly we do with any given partner isn't some script we follow, or determined based on what sets of chromosomes or genitals are in the mix, it's about exploring our unique sexuality and theirs, communicating, experimenting, and varying what we do, and how we do it, based on mutual wants, needs and preferences.
Gay Man answering a Lesbian Question LOL