Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
The Prophet (Sallallahu Alaihi wa Sallam) said: "whoever makes Ghusl (ceremonial washing) and wears his best clothes, some perfume if he has any, then comes to the Friday prayer without stepping over other's necks to get to the front rows, then prays what Allah decreed for him to pray, then listens from the time the Imam starts the Khutba until he finishes it, his sins will be forgiven between this Friday prayer and the previous one." Reported by Abu Dawud.
As regards after Friday prayer, the Prophet (Sallallahu Alaihi wa Sallam) incited people to pray 4 raka'as after it as he (Sallallahu Alaihi wa Sallam) said: "Whoever wants to pray after Friday prayer, pray 4 raka'as." Reported by Muslim.
It is permissible for you also to pray 2 raka'as only after Jumua (Friday prayer). Muslim reported in his Sahih that Ibn Omar narrated that the Prophet (Sallallahu Alaihi wa Sallam) used to pray 2 rakaats after Jumua.
Therefore, we advise the questioner to continue to pray what he used to pray before and after Friday prayer.
With regard to the meaning of "Jazaka Allahu Khairan," it is a Dua from Allah to give good to a person in return of the good deeds that he had done.
The difference between "Jazaka" and "Jazakum" is that "Jazaka" is used for a singular person whereas "Jazakum" is used for plural.
Allah knows best.