How do we know what letters to use for words?

There are a lot of letters that sound the same (Dah vs Daad for example, or Zah vs Zal.. ) and how do we know which one to put in a word? For example I would spell "ahlan wa sahlan" Aleph-Heh-Lam-Noon Waw Seen-Heh-Lam-Noon cuz i thought it sounded like A-H-La-N Wa Sa-H-La-N... was this incorrect? 2. Also like in "betitkalem" why is it beh-teh-teh-kaaf-lam-meem" instead of "beh-teh-TAH-kaaf-lam-meem"?

3. in "Saba7 il 7'eer" why does it start with "Saad" instead of "seen"? because "seen" has been used for a "sa" sound, like in "samaka"..

Hi TC It's very difficult to romanize Arabic since English doesn't have the exact same sounds. The best bet is to use the Arabic letters for accuracy. Native Arabic speakers would know whether to spell words with a saad or seen but it's difficult for Arabic learners to know which to use especially if they still aren't able to hear the difference between the letters. Also, many dialects pronounce letters in a "lazy" way so already similar letters end up sounding the same! For example, the letters saad and seen both end up sounding like a generic "s" sound. Natives would know which letter it's supposed to be but it makes it hard for students! I would suggest looking for the correct spelling of words that you aren't sure about. I hope that helps! - Amira