I have a question that might be very trivial I have encountered this kanji sai 細 I wish to know can I use it this way. 話の細-the details of the story
When a kanji has a particular meaning that does not mean that you can just use that kanji alone as that word. I have to question how much you investigated this to begin with, as any simple translation or dictionary lookup of "details" will get you several options. In this particular case you could say 話の詳細. Notice that 詳細 contains the kanji in question.