How do I connect LEDs in a parallel?

The circuit you have shows a current driver IC. The simpler way is using ballast resistors. You can't just hook up the LEDs themselves in parallel because they have slightly different characteristics; although they all drop approximately 3.4 volts that voltage varies a bit, and some LEDs will hog the current. You have to connect the 12 volt strings in parallel so the ballast resistors also function as equalizing resistors. The first source shows exactly how to do it.