The Macronutrient breakdown is found next to the Energy Summary on the Diary page.
To change your Macronutrient targets, navigate to the More tab > Profile + Targets. Learn more in the article Macronutrient Targets.
The percentages listed within the Macronutrient Target bars indicate the percentage of your goal for each macronutrient. By default these bars will show your macronutrient breakdown for all items logged in your diary.
To see the macronutrient breakdown of a specific food or multiple foods, make a selection in your diary. The Macronutrient target bars will fill up based on the item(s) you have selected. To revert back to complete day breakdown, click on your selection again or click elsewhere in the diary screen.