Then, will you , please, explain to me why you use a "Y" in Zayd and "E" in Tamer a transliterate a letter my ear hears the same way? Particularly, why "Y" ? Because it looks more fancy? I realize that the "i" in Tamir is only a diacritical mark, but the sound is the same, only more or less long or emphatic. And, by the underline it uses, the AI incorporated in my computer's spell check likes your "Zayd" no better than my "Tamer". Are these just totally arbitrary conventions?
Whenever you see "shadda" it means you have to stress that letter. As an example, the word حمام حَمَامْ=pigeon Pronounced as hamam حَمّامْ= bathroom Pronounced as Ham-mam as if it's حممام=> حمّام
Another exmple: درس دَرَسَ=studied Pronounced as darasa دَرّسَ=taught Pronounced as darrasa as if it's دررس=> درّس
So the shadda basically guides you how to pronounce the word.
Hope this helps