'devochka' is more closely to original 'девочка' in public, but in private conversation with girlfriend, russian boyfriend can say 'dyevochka moya' using as much 'y' before 'e' as needed )) generally, russian 'e' is short sound )

They simply show you that you should soften the consonant before the vowel "e". Because, in Russian, you often need to soften consonants which stand in front of such vowels as е, и, ю, я. If some foreigner read the word девочка spelled as devochka, he can probably read it as дЭвочка. So, they spell it liks dyevochka to show that you should soften your "d" before sayng "e". So, you don't pronounce the two letters as two different sounds "ye". You just make your "d" soft. D'evochka.

No. (` is for stress, ' is for softness) Е is pronounced as [йэ] !if stressed! 1) in the beginning of a word: ем [йэм], ей [йэй] 2) after ь and ъ: подъезд [падй`эст], колье [кал'й`э] if unstressed e is pronounced as something between [йэ] and [йи] 1) in the beginning of a word: енот [йин`от], еда [йид`а] 2) after ь and ъ: ученье [уч`эн'йи], подъезжал [падйижж`ал] BUT after consonants 1) if stressed e is pronounced as [э] and the previous consonant goes soft: место [м'`эста], нет [н'эт] 2) if unstressed e is pronounced as something between [э] and [и] and the previous consonant goes soft: тебя [т'иб'`а], меня [м'ин'`а], there is also a sound which is similar to the last vowel of "water" and "bigger" - reduced [э], which you can hear in unstressed posisions after hard consonants, like this (I will type is as э, but actually it's shorter and weaker than э): солнце [с`онцэ], тише [тишэ]