The current level and its target.
The Boosters that you can select ( grayed ones cannot be used on current level ) and how many do you have of each one ( The top left corner of each booster). Note that to select/deselect a booster, you need to click on it. Selected boosters have a green mark on them as shown above. More on Boosters here
To the right, you will find the High scores of your friends alongside a heart shaped button with a letter in it, which you can click to send a life to your friend.