It's a measuring cup for making alcoholic drinks.
The measuring cup comes in two sizes 15 ml and 20 ml, which allows you to mix many kinds of drinks.

Drinks

Aperol Spritz

• Aperol (80 ml)
• Dry Prosecco (120 ml)
• Lime (1 pc)
• Soda (40 ml)

Cuba Libre

• Ice (4 pcs)
• White rum (40 ml)
• Lime (1 pc)
• Cola (200 ml)

Long Island Iced Tea

• Gin (20 ml)
• White rum (20 ml)
• Vodka (20 ml)
• Triple Sec or Curacao (20 ml)
• Lemon juice (20 ml)
• Coke (amount depends on your taste)

Mojito

• Lime (½ pc)
• White rum (100 ml)
• Mint (8 leaves)
• Brown sugar (3 tsp)
• Soda (15 ml)
• Ice

You can find some more drinks here: https://www.winehouse.cz/michane-drinky/

Sorry I couldn't find an english page :D