I'm guessing that you're asking how the Friar proposes to help Juliet out of her quandry, but I'm going to respond to what you've actually asked here, because I think it is more interesting.
He first helps her by agreeing to give her (and Romeo) her hearts' desire by marrying them quickly, without parental consent.
The second thing he does is to devise a plan that would interfere with her marriage to Paris, although arguably, he may be proposing to "help" her when in fact what he attempts is to help himself.(If the marriage is uncovered, he may be in serious trouble).
Finally, the answer to your question, most likely, is that he plans to give her a potion that approximates death so that she can be too "dead" to be wedded to Paris, she will fall into a deep, comatose sleep, and she will wake up later, and carry on. The Friar's plan is to send word to Romeo so that he can come back in time to be there when Juliet awakens.