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.

In Shakespeare's Romeo and Juliet, how does the Friar propose to help Juliet?

In act 4, scene 1 of Shakespeare's Romeo and Juliet, the title character Juliet goes to Friar Laurence for consolation because her husband Romeo has been banished from Verona and her parents have just betrothed her to Paris. She is expected to marry Paris in two days and is at a loss for what to do because she is already married. Naturally, marrying a second man would be a sin, and she threatens Friar Laurence with the second sin of suicide should he be unable to find some way to help her.

Friar Laurence proposes that she tell her parents she is willing to marry Paris and then, the night before her wedding day, drink a vial full of a liquid that will stop her pulse, her breath, and her blood flow, making her appear to be dead for 42 hours. In other words, his plan is to help her fake her own death, as we see in the passage:

Take this vial, being then in bed,
And this distilled liquor drink thou off;
When presently through all thy veins shall run
A cold and drowsy humour; for no pulse
Shall keep his native progress, but surcease;
No warmth, no breath, shall testify thou liv'st. (V.i.95-99)

The rest of Friar Laurence's plan follows: he'll inform Romeo of the faked death and have Romeo meet her in the Capulets' family tomb, where they will bury her once they believe her to be dead. Then, Romeo will carry her off back to Mantua, where they will live happily as husband and wife.