I have missed some Salaat many years ago but am unaware of how many.

Answer

Regarding missed Salaat, you have to reflect deeply, then make an estimate as best as you can of the number of Salaat you think you have missed. For example, after reflecting, you come to a conclusion that the number of Salaat could be two years. Make a note of this. Then start performing Qadha of one, or two, or three or as much as you wish at a time. Start with Fajr, then Zuhr, then Asr, then Maghrib, then Isha, then Witr as well. This gives you qadha of one day. Record the one day in your note book. Whenever you perform Qadha, make a note. Perform it in the sequence mentioned above so that it is easy to record a day. In this way continue until the Salaat of the 2 years is completed. Whenever beginning a Qadha, make niyyat as follows: "O Allah! I am making the first Fajr qadha of all the Fajr Salaat which I had missed." If it is Zuhr, then mention Zuhr. For each qadha mention this very same niyyat because every Qadha you will be performing will be the first of the balance you owe Allah Ta'ala. You need not verbally utter the niyyat. You may just intend it in your mind.