Pronunciation
It is a so-called iotated vowel and typically sounds as /ja/ in initial or post-vocalic position, something between English pronunciations of ⟨ya⟩ in 'yard' and 'yack'.
Another case in when ⟨я⟩ follows a soft consonant: no /j/ sound occur between the consonant and vowel.
Exact pronunciation of the vowel sound of ⟨я⟩ depends also on the succeeding sound due to allophony in Slavic languages. Before a soft consonant it is, the near-open front unrounded vowel – like in 'lamb'. If a hard consonant follows ⟨я⟩, or none, then the result is an open vowel, usually – like in French 'la'. See palatalization #Synchronic palatalization for some background.
In non-stressed positions the reduction depends on language and dialect. The standard Russian language reduces this vowel to, but in yakanye dialects ⟨я⟩ does not reduce at all, although other instances of the /a/ phoneme (represented with the letter ⟨а⟩) do reduce.
in Bulgarian the vowel sound is reduced to /ɐ/ in unstressed syllables, and is pronounced /ɤ̞/ in stressed verb and definite article endings.
Read more about this topic: Ya (Cyrillic)