Free to play games consists of you getting 5 new tickets a day to read the story (either all at once or one every 4 hours), lessons/battles in order to gain experience points and in-game money, and events (collection or story).
You will also encounter experience points checks and clothing checks while reading the story. Clothing or Avatar Checks will give you the option to either buy a premium story with a currency that can be purchased with real money or a normal story that can be purchased with the in-game money that you earn from lessons/battles.
Free-to-play games can be played 100% for free. Your first route in a F2P game will almost ALWAYS be tough and you may reach clothing checks and be stuck there for a while.