Now that you've created collections of recipes (see here), you can use those recipes in your meal plans! Here's how to add recipes from your cookbook or collections to your meal plan.
Click 'Create' (1) on the upper left corner of the screen and then click 'Meal Plan' (2).
After you fill in the title, description, tags, and dietary restrictions of your new meal plan (more about this here), click Save. Scroll down on the page and click 'Add/Edit Meals' (3).
You will now see the scheduler screen. Click on the + next to any meal or snack under any day to put a recipe into that slot (4).
You can filter recipes (5) just under the search bar to see only recipes created by you or in your collections. Now you can choose any of the recipes from your collection to add to your new meal plan.
You will now see only your recipes. Click on the photo of whichever recipe you would like to schedule into your meal plan for that meal or snack.
On the left side of the page, you will see a drop down menu, click that to choose which collection you'd like to see recipes from. (6).
Now you can chose whichever recipe you would like to schedule from that specific collection. For more details on scheduling recipes, see here.