If two trains move in same direction on parallel rails, if you are sitting in fast moving train, you will think to appear slower moving train is like going reverse direction. That is what retrograde motion of planets means and when a planet move backwards it is called Retrograde planet.
Planets always move in forward direction, they never move backward ( or Retrograde),but because of their relative movement with respect to earth, sometimes they look like moving backward ( Retrograde).
If a planet is in debilitation(neecha), but is in Retrograde motion, it will give results as if it is exalted (full power).
If a planet is in exaltation(uccha), but is in Retrograde, it will give results as if it is in debilitation (zero power)
If the Retrograde planet is near to the debilitation sign, then also it will act like an exalted planet and will give very good results to the native.
If the Retrograde planet is near to the exaltation sign, then also it will act like debilitated planet and will not give good results.
For example: If you have Jupiter in Capricorn and is Retrograde, even though Capricorn is neecha rasi for Jupiter being Retrograde it will give exalted power and good results to the native. On the contrary, if Jupiter is in Cancer which is exaltation sign, but if Jupiter is Retrograde, it will like Neecha and will have no power and will not give good results.
Practical (live) Example:
Most Powerful Prime Minister of World-Shri NARENDRA MODI-Prime Minister of Republic of India is having Jupiter in Aquarius and is Retrograde. Aquarius is closer to debilitated sign Capricorn, but Jupiter being Retrograde, it became like boon in disguise. More the retrograde planets in a birth chart, higher will be the positions in life. Shri Narendra Modi has two retrograde planets.
But Retrograde planet near to exaltation sign can create havoc:
If we discuss about Shri Mlujibur Rehman -former president of Bangladesh, he has two Retrograde planets-Retrograde Saturn and Retrograde Jupiter. Natural malefic Saturn turned in to an overall functional benefic and during Retrograde Saturn Mahadasa, he became President of Bangladesh. But his 8th house was heavily afflicted by Mars, Rahu and Ketu which caused violent and sudden death during Saturn’s dasa itself( 4th sub lord). Saturn was near to its exaltation sign and retrograde, so it killed him during the same dasa