1. ADA and PUNYA: both have different meanings actually.., but ADA can be used to subtitute PUNYA and vice versa.
for example:
a. PUNYA : Kamu punya uang tidak? (You have money or not?) / Apa kamu punya uang? (Do u have money?) ->PUNYA means own. PUNYAku (my own). So, I was asking 'do you own money'?
b. ADA : Kamu ada uang tidak? (You have money or not?) -> this sentence means 'do you hold money?', ada means exist/ there is. So, no matter the money is yours or not, but THERE IS money.
2. BAIK and BAGUS: (fyi, baik has so many meanings (kind, alright, good, etc). but if compare to bagus, so the meaning is 'good') -> both mean 'good'.. Baik = good/ great. bagus= good/ beautiful/ nice. The meaning depend on your sentence.
for example:
a. Buku itu bagus (the book is good (beautiful). -> you can't say buku itu baik for this sentence.
b. Meskipun komputer itu sudah tua, tapi kondisinya masih baik OR bagus. (Even though the computer is already old, but the condition is still good)
So, usually when you describe the condition of a product, you use 'baik' -> Kondisi barang yang baik, when you describe the appearance of a product you say -> bagus (nice/beautiful), when you describe the quality you can say both -> Kualitasnya bagus/ kualitasnya baik.
3: MEMPERBAIKI dan BENAR: different function.
MEMPERBAIKI (verb): to correct/ to fix. -> Ayahku sedang memperbaiki mobil (My father is fixing the car) // Aku sedang memperbaiki/mengoreksi tulisan adikku ( I am correcting my sister's writing)
BENAR: correct/ right. -> Jawabanmu benar semua! (your answer is all correct!). Benar sekali! (absolutely right!)