I can't understand some special cases in kanji readings

[Sharkolese]

Hello all :D

I'm still a beginner trying to learn Japanese :-), and I'm struggling in understanding how some Kanji compounds are supposed to be read individually。

For example, this word: http://jisho.org/word/%E4%BB%8A%E6%97%A5 (today), can be read as こんにち as I can see? (or does this mean something other than "today"?), anyway I can see that 今 has one of its readings as こん and 日 can be read as にち so that's not my problem, but the problem is that the way I learned to read "today" is きょう which also has the same Kanji 今日 , but the thing is, I can't find any readings for each of the characters that can compose any pronunciation even near きょう 。can someone please explain? 。

I'm sorry if this might seem like a novice question to some of you, but as I mentioned above, I'm still a beginner :-)　。