You do one of the consecrations - usually either the 33-day Louis de Montfort one, the 33-day “33 Days to Morning Glory” one, or the 9-day Maximilian Kolbe one. Whichever one you do is supposed to end on a Marian feast day or the day before.
Then you have to renew it every year (you can use a different method the next year, like if you did 33 day initially you can do a 9 day the next year).
The idea is to love Mary more and be closer to her. And in doing that you will love God more.
The consecration involves saying certain prayers and doing certain readings every day for the specified time period.
Once you have finished the consecration, you say a really short prayer to Mary every day just saying you renew your consecration to her and you offer her all your indulgences and good works for that day along with yourself so she can use you to carry out God’s plans.