A. First Taubah (repentance) should be made for previously neglecting Salaah.
Make a note of the amount of Salaah missed and begin fulfilling those missed Salaah. Qadhaa (fulfilment of all the missed Salaah) is compulsory. If you are unable to recall the exact amount of Salaah missed, then an estimate will also be valid.
The method of Qaza Salaah is the same as Salaah performed on time. Specify ‘Qaza’ in the intention. Qaza will be made of all Fardh Salaah and also the Witr of Eshaa. Qaza will not be made of the Sunnah Salaahs.
If you have missed many years of qaza and you now made tauba and decided to make qaza of all, then you should make one qaza with every ada salaah. Write down how many qaza you make a day. When making intention say: O Allah I am making my first qaza of zuhr salah, or the first qaza of fajr, etc. Say the same intention for every salaah.
Multiple qaza on one day is also correct.
May Allah Ta’aala make it easy for you, Aameen.
Mufti Siraj Desai