I suggest you read about how to pleasure yourself. There's a certain area in females that is the "arousal" area--the clitoris. Arousal is evident when the vagina starts lubricating. It starts happening on its own in women when they are interested in sex. Yes, nipple erection can be part of it, too. But that can occur for other reasons, such as being chilled.

I suggest you try it on yourself, if you want to. But if you don't feel so inclined yet, then don't worry about it. (I don't know how old you are.) Females take longer to get aroused than men do. I encourage you not to have sex for the sake of just saying you had it. There's no shame to being a virgin. In fact, in my book, it's something to be proud of in this day and age. (I am a married lady of 60.)