I am a newbie into stock trading and I am stuck with many doubts in myhead, please help me.

Is it compulsory to register in cdsl or nsdl?
Will NSE send us any letters to our address, my concern is that I recently changed to a new address and my old address is registered with my trading and Demat account. Someone please clear my doubts.

Thank you

Yes, if you are dealing under Equity intraday or delivery trades. Since you are a newbie, please go through varsity chapters.

No. However, if you wish to change your address, you can do it by doing account modification procedure