If you don’t find this game’s interface simple and easy to understand, then I don’t know what is. The icon at the upper left portion of the screen is where you get to access the different worlds. At the upper right portion of the screen, are your current resources. Right beside it, you have a shortcut to the basic credit (name of the premium resource in the game) packages, special offer combo packages (includes power attack items plus credits), or the option to watch advertisement videos in exchange for a bit of the in-game currency (credits).
On the bottom left portion of the screen, you’ll see the current hero enlisted for your missions. You can click on this icon to pick a hero, and/or passively upgrade them whenever they level-up. And then there are also the 3 icons on the bottom middle part. The wrench icon lets you access the Passive Upgrades you could purchase for your units, the rocket icon beside it is where you get to purchase and equip Special Items that you can use to call in a backup move/attack whenever you’re in a pinch in the game.
The medal icon beside it houses all the achievements that you can earn in the game – from which you also get bonuses for achieving them. Lastly, you have at the bottom right corner of the screen a settings sub menu from where you could tweak your difficulty mode, sound, and graphic options for the game, as well as a “clear progress” option.
On the center of the screen, you’ll see the map of the planet that you are currently in and access the stages for that particular world. Although unnecessary, you also have the option to pinch zoom on the world to have a closer view of its details. See the video below to get a feel of how its basic interface is put together and the extent of every options found there.