[IssuessBratte]

Salam

if you missed a wajib portion of your prayer for example
1. you forgot to sit in tashahud after your second rakat (and you were praying a 4 rakat salah)
2. you forgot to make takbeer and qunoot in your witr,
3. you were praying a non fardhs salat and you forgot to read an additional surah after fatiha in the 3rd or 4th rakat

then at the end in when you are sitting in your final tashahud immediately after reading the kalima (while rasing your finger at the appropriate place), make salam once just to your right side (but not to the left)

the single salam is followed by two sajdahs after which you sit (qaida position) read your tashahud, durood, dua then make your salams as normal.

sajdah is not made for actions that are only considered sunnah and not wajib.

there is probably more to add to this and someone more knowledgeable can contribute.