Okay, I'm filipino so I could correct a few errors.
One thing you got wrong is that it goes the other way around. Kumusta ka is the informal way while Kumusta po is the formal way. Also, Kumusta po can also be written as Kumusta ka po. There won't be any difference in the basic meaning of the phrase. The word 'na' can also be added before the 'ka', like "kumusta ka na", or "kumusta ka na po".
How to use kumusta ka/po
to an older sibling, parent or figure of authority: Kumusta ka po?
to a friend or acquaintance" Kumusta ka?
A greeting, which in English means, "How are you?" It is often replied to with, "Mabuti," which means good or fine.
Usage of "Kumusta ka/po"
Po is a term that is used to show respect. That is why:
- "Kumusta ka?" is INFORMAL and is used among friends or when addressing a younger person.
- "Kumusta po" or "Kumusta ka po?" is FORMAL and is used when addressing an older person. In fact, the best way to say it is "Kumusta po kayo?" using the formal/plural you (kayo) instead of the informal/singular you (ka).
- "Kamusta" is a popular but wrong way of spelling "kumusta."
Tagalog for "How are you?" Kumusta ka is formal and kumusta po is informal. Notice it is very similar to the spanish "Como esta?" Thats cuz the spaniards occupied The Philippines and a lot of Tagalog words are similar to spanish.
I dont speak Tagalog but i know that much. If i am off with my definition please correct me.
teacher/cop/respected elder- Kumusta ka?
friend/younger person- Kumusta po?