EXP Tickets are a type of item obtainable in Battle Girl High School. These can be obtained in various ways, for example, as a reward for completing Objectives in some Missions.
The amount of EXP Tickets you have collected can be reviewed in your Bag.
You can access your Bag from the main menus by simply tapping the MENU button and then tapping the button with a bag icon. From there you can read the number of EXP Tickets you collected as well as access the screen where you can use them.
This screen can also be accessed by tapping the icon at the bottom-center of the screen, and then tapping the rightmost icon.
If it's the first time you access this screen, you'll be presented with an explanation on how EXP Tickets work.
How to use EXP Tickets Edit
EXP Tickets are used to transfer the amount of EXP gained by a card into a different card of the same character that has an equal or higher amount of stars. By the end of this process, the card that gave out the EXP will be reverted back to Level 1.
Be warned that the receiving card won't necessarily rise to the same level of the card that gave the EXP. That's because cards with a higher number of stars need more EXP to level up.
In order to prepare the cards for EXP transfer, you must first select either the card you want the EXP to be transfered from or the card that you want the EXP to be transfered to. Once you selected either of those, the other card slot will only show the cards for the character you chose and highlight only the cards that can be used to complete the process.