Can someone please explain me how did it happen? What were the reasons? What was the driving force for it to be proclaimed? I am intrested in that topic, but I do not know a lot about it and I know this is the best subreddit to get valuable information about that question!
The 5-second overview is that there was a Jewish nationalism called Zionism which took off in the early 1900s. Momentum and international pressure eventually pressured the British (who were in control of the area) to withdraw from Palestine, and with the UN's consent the Jewish Agency declared Israeli independence. When the dust of the War of Independence cleared, Israel existed.
I'm mostly giving that summary as a way of asking what you're specifically asking about. It's a pretty broad question.
If you're looking for the Jewish ideological forces which propelled it into existence, see here. If you're looking for the complex conflict between Jews, Arabs, and British in the pre-state days, which gives background into the environment of pre-independence Israel, see here.