where is start the first revelation?

The revelation of AL-Quran started in the month of Ramadan

During the year  610 AD at the time prophet Muhammad(P.B.U.H)

was in a cave called Ghar e Hirra on the jabal-un-Noor or the

mountain of light near makkah jibreel a.s continued to teach

prophet Muhammad (P.B.U.H)passages of Al Quran every

now and then.

The revelation continued Throughout  the following 23 years

of the life of prophet Muhammad (P.B.U.H) until he passed

away.

At that point revelation of Al-Quran was completed.