Welcome to the discussion forum, ashish.gohel!
It will take some effort to get an answer to your question. The Buddha said that both views that “there is a self” and “there is no-self” are wrong.
You may want to read in the following order:
What Reincarnates? – Concept of a Lifestream
“Self” and “no-self”: A Simple Analysis – Do We Always Act with Avijja?
Anatta and Dukkha – True Meanings
A “lifestream” per first post above can be thought of the following way too. One has a set of gati (soemtimes spelled as gathi). These are character qualities/habits that change from life-to-life and even during a given life. One attains Nibbana when one gets rid of all gati. You can learn about gati by starting with the following post: “The Law of Attraction, Habits, Character (Gathi), and Cravings (Asavas)”
Then you can use the “Search” box at top right to find more posts on gati. Please feel free to ask questions (and refer to the posts in question) as you proceed.