When building a workout you'll have the option to set different male/female characteristics for each of the movements. After the different characteristics are set, the site will only display the appropriate characteristic for each member. For example, if a female member logs into the CrossFit btwb app and attempts to post a result for Fran, 65# will be displayed because the app will recognize the account as belonging to a female.
In order to set different weights, go through the workout building process. Add a movement that has a weight component and click the "vary for women" link. Enter the different weights. The first number is for the men, the second is for the women.
The description will be updated to show the varying weights.
You can also make male/female distinctions for the reps, distance, and height characteristics for each movement. Follow the same steps for adding female weights above.