What do you know about sajda-e-sahwa? when is it valid and when its not?
Re: Sajda-e-sahwa
sajda e sahv is due when you miss or do something in error of the farz arkaan of namaaz or if you have done something extra. one must know the farz parts of the namaaz to be able to do sajda e sahv as the need arises.
Re: Sajda-e-sahwa
sajda sahaw becomes obligatory, if ...
- you delayed the farz rukn of your salat (by making an error, hence repeating it - or doing an act like sitting in tashahud after 1st rakat which delayed your act of 2nd rakaat)
- or missed the wajib rukn of your salat -
As KKF said, you should know the farz and wajib arkaan of salaat.