According to Prophet Muhammad (sallallahu alaihi wasallam) after the seventh verse is recited we should say Aameen and if our aameen coincides with the Aameen of the angels then all our sins will be forgiven.
Hadith from Sahih al-Bukhari, Sahih Muslim, Jami’ at-Tirmidhi, Sunan An-Nasai, Sunan Ibn Majah
Narrated Abu Huraira (radi allahu anhu): Allah’s Messenger (sallallahu alaihi wasallam) said, “Say Amen when the Imam says ‘Ghairi l-maghdubi `alaihim wala d-daalleen’ (not the path of those who earn Your Anger (such as Jews) nor of those who go astray (such as Christians)); all the past sins of the person whose saying (of Amin) coincides with that of the angels, will be forgiven”.
Hadith from Sunan Ibn Majah
It was narrated from ‘Aishah (radi allahu anha) that the Prophet (sallallahu alaihi wasallam) said: “The Jews do not envy you for anything more than they envy you for the Salam and (saying) ‘Amin’.”
Aameen means “O Allah (subhanahu wa ta’ala), please answer the Dua”. Another meaning is, “Let it be so”.
According to Prophet Muhammad (sallallahu alaihi wasallam) this is the only action in the prayer which is done along with the Imam. All other actions like going to the ruku etc are performed by Imam first.