How to experience Karma? Today I realize that , If something good or bad happen to me is caused by Karma. It gave me a huge relief. Because,Before I got aversion when something bad happen to me. But now, I believe that I am 100% responsible for whatever happen to me.

But, As I know, Not everthings are caused by Karma. There are some other reasons such as whether, Dhamma etc. So how can I know the real cause behind something for sure? (It is Karma or other cause)

It is said that Someone needs to experience the truth to understand the truth. So How can build a solid understanding of the cause behind things and Karma ?
Yes. It's true that not everything is caused by karma. Some things are caused by other reasons, like the weather. The Sivaka Sutta talks about this. There's a summary at the bottom:


  Bile, phlegm, and also wind,
  Imbalance and climate too,
  Carelessness and assault,
  With kamma result as the eighth.


The Acintita Sutta states that you can't work out karma and its results precisely:


  "The [precise working out of the] results of kamma is an
  unconjecturable that is not to be conjectured about, that would bring
  madness &amp; vexation to anyone who conjectured about it.


What's more skillful is to develop one's virtue (sila), concentration (samadhi) and wisdom (pañña) as stated in the Lonaphala Sutta. That will mitigate the ill effects of past karma.