In the meal planner, use the left sidebar to view your recipes.
To the right of the recipe name is the handle icon. If you click and hold the handle you will be able to drag the recipe onto the Planner and drop it to a day and mealtime.
If you click on the recipe name, the recipe details will appear.
On a tablet will need to tap and hold on the handle icon with some intention, so your tablet recognizes you are wanting to drag the recipe instead of scroll the recipe list.
I can't figure out how to hold it so that I can drag it.