What does it mean if a girl does not get wet enough to have sex?

get some lube

you have to invest more time in foreplay. tell her she's beautiful and sexy, run your hands over her body and tease her with kisses and your touch, don't go straight for it, run your hands around her thighs and breasts, kiss her all over until she's begging for you to touch here down there, then don't go straight for fingering, tease her a little more with differnt pressure of touch and different movements. experimenting is the key here so just ask her what she is comfortable with and just take it slow until you find her on switch

Use saliva, or invest in some lube.

With woman sex and relationships are all about psychological and emotional needs. For men things are largely physically based, especially when it's about sex.

If she doesn't become "ready" physically, then she probably isn't being satisfied emotionally. More proper foreplay could help in those moments, you're never going to get anywhere just by going right for it. It's like a rollercoaster, you have to wait in line and take your time getting to the front before you can really have your turn. But it also may require even more than that extra intimacy, you may have to show her more true commitment that is NOT related to sex. In other words spending extra time on foreplay only shows you're spending your extra effort on sex, when she wants to see you spending extra time on other things just because you care. By doing things that aren't really going to get you laid you will get laid. You might think buying flowers and cleaning the house has nothing to do with getting laid but it's exactly those things that will get you laid.

It means you haven't used enough lube.