Game Start is the menu selection for starting a new game.
After (?) inputting your mane's name, you can configure the game's setup and your character:
Max Level: The maximum level your character can reach. Be sure to not accidentally select the wrong setting here!
Difficulty: Strongly influences how hard the game will become. For beginners, normal is strongly advised. Enemies drop more items on higher difficulties.
Death penalty: Enables or disables loss of exp and bits (currency) upon death. Most of the time, you will still advance on both even if you end up dying.
Enabling Death Penalty increases the chance enemies drop items.
On the character selection screen, you can choose how your character looks like, as well as the race - Every race ("type") has different strength and weaknesses, skills and gameplay. If you have unlocked them, you can press attack on Earth, Pegasus or Unicorn to switch to
(Spoiler box) Foal, Bat Pony or Alicorn (the latter not implemented yet) (End spoiler box)
While in the Mane selection setting, pressing attack on having chosen the corresponding mane style will switch everything to a mane6-preset if applicable.
If you don't like any of the included cutie marks, you can draw your own in the game on a 5x5 pixel panel.