Planets are retrograde when in the course of their orbit around the Sun they appear from the Earth to be transiting backward. During these periods many people experience the influence of the planet as more internal and often have to revisit, relearn or redo certain decisions, conversations, events or problems ruled by the planet that is retrograding.
For example, during Venus retrograde you might need to put some work into relationships you have been neglecting. In this way a retrograde period can be seen as an opportunity to go back over old ground and repair any missteps we have made.
Those who were born during a planet’s retrograde phase will experience this energy throughout the course of their lives, more or less so depending on how powerful that planet is for them personally. In this case the entire lifetime could be seen as an opportunity to relearn certain lessons or redo certain experiences.
I hope this gives you greater clarity on the retrograde process. It’s quite complex and others may like to chime in with their own experiences.