1. Supaya.
Supaya is a conjunctive, it means "So that..." It always be followed by a reason or statement that supports the main sentence.
Example:
- Dia giat belajar untuk ujian akhir, supaya mendapat nilai bagus.
- He studied hard for the final exams, so that he would get good marks.
The synonym of supaya is "agar".
You can substitute supaya to agar freely (no special rules).
2. Jadi.
As a conjuntive, jadi means "So"
Example:
- Kami tidak membawa cukup uang saat itu, jadi kami tidak bisa membeli anak anjing kecil yang lucu itu.
- We didn't bring enough money back then, so we couldn't buy those cute little puppies.
Synonym of jadi (as a conjunctive) is "Sehingga".
You can substitute jadi to sehingga freely (no special rules).
As a verb, Jadi (or menjadi) means "become"
Example:
- Setelah minum segelas susu, bayi itu jadi diam.
- After drinking a bottle of milk, the baby became silent.
3. Begitu has so many meanings depends on the context.
As a adjective, it means "Such".
Example:
- Saya belum pernah melihat gadis yang begitu cantiknya.
- I've never seen such a beautiful girl.
As an adverb, it means "So" or "Very"
Example:
- Dia begitu tampan dan sangat menarik.
- He's so handsome and very attractive.
Synonym of begitu (as an adverb) is "Sangat".
You can substitute begitu to sangat freely (no special rules).
Begitu also means "like that" or "that way".
Example:
- Apa benar begitu?
- Is it really like that?
As an interjection, it means "I see..."
Example:
- Jadi, dia sudah tahu? Begitu ya...
- So, he already knew? I see...