Help with Burmese writing

Hi,

I am a Sri Lankan studying Burmese writing (to read Pali written in Burmese). I have a couple of questions about the writing system that I'd love to get clarified.

  1. ဝါ vs. ရာ - vowel signs for long a

I'm not sure which sign to use for which letters.

  1. သု vs. က္ခု - vowel signs for u

again, I'm not sure which letters use the short, vs. the long version.

Thank you in advance!

  1. Are there any other vowel signs that change based on the preceding letter?