Part of your answer is the offset column, which seems to be relative to the abbreviation used. This implies, to me, that each particular abbreviation has it's own way of specifying the "starting point" of the time. Added is the DST flag, which (probably) tells you that your app needs to keep daylight savings time in mind.
I can't tell you why there are so many, or which one to pick, but there you go. Just, you know, pick one, learn it's rules and stick to it. -- Bier met grenadyn Is als mosterd by den wyn Sy die't drinkt, is eene kwezel Hy die't drinkt, is ras een ezel
