Romeo and Juliet meet at Juliet's home, when Romeo sneaks in to get close to his lady-love, Rosaline. All that "lady-love" business changes, however, when he sees Juliet.
There is much imagery in the words they exchange when they finally meet (Act I, scene v). You should also know that these 16 lines of dialogue are in sonnet form, which signifies the harmony between the two of them. The picking up on and playing off of each other's imagery also shows this.
Romeo first calls Juliet a "shrine," suggesting that he kiss the shrine to make up for any harm caused by his touch. And, since Romeo has referred to her as a "shrine," Juliet calls Romeo a "pligrim," which, in Shakespeare's day meant an religious traveler. If you think of the Puritans who travelled on the Mayflower to America that we still refer to as Pilgrims, you'll see what I mean. So, if Juliet is the shrine and Romeo is the pilgrim to the shrine, she is a very holy thing indeed, and Romeo is but a poor sinner seeking redemption.
He's also a teenager seeking a kiss. He opens asking for a kiss -- "to smooth that rough touch with a gentle kiss." And then when Juliet moves herself up the religious ladder, referring to herself as a "saint," she tells him that "palm to palm" -- the conventional gesture of prayer in Christianity -- is the only kiss allowed. But Romeo, still after his kiss, asks that "lips do what hands do" and thereby gets his kiss.
They exchange some witty banter about sin going back and forth when they touch lips, and then Juliet breaks the mood by saying that Romeo kisses by "the book." And Shakespeare could mean a couple of things here, the most obvious being that Juliet thinks Romeo has been reading too many "How to Get the Girl" manuals, and is following the kissing rules. Alternately, she could be making reference to how Romeo used The Book (the Holy Bible) as a means to an end.
Later, in the dark of the balcony scene in Act Two, when Juliet can't see Romeo, only hear his voice, he tips her off as to who he is by calling her "fair saint," yet again.