Hi Nunu,
This is a very basic question.
1) If you are creating a material, you will enter material ID.
2) The Breakpoint is on Line 14 as visible in screenshot in GET_INSTANCE method.
3) The BADIs are part of enhancement framework & are sometimes feeded with certain parameters from transaction ease the usage. You can explore BADI's signature to know more about the same.
Thanks,
Ravi