This screenshot is from a level 110 player (max level). It has all the game features unlocked. When you start playing, you will have fewer menus.
The menus are quite self-explanatory. Some of them have a sub-menu inside, such as Story. And some of them only appear at certain times or events, such as Limited Time Partner.
Obviously, the purpose of this game is to get rewards by doing tasks and missions, to get better and stronger ninjas and build them. As your ninjas get stronger you can do more difficult tasks and missions and get better rewards, and so on.