Am I correct in understanding that there is no Sunnah (recommended prayer) before the Friday prayer, and that whoever prays in the mosque prays four rak'ahs of Sunnah after the fard (obligatory) prayer, and whoever prays at home adds two rak'ahs of Sunnah before the four rak'ahs? And what is the classification of these rak'ahs, and are they Sunnah Mu'akkadah (confirmed Sunnah)? And is it permissible for me to pray two rak'ahs of nafl (supererogatory prayer) after the Friday adhan and before the khutbah, even if it is not a Sunnah Ratibah (regular Sunnah), to avoid embarrassment?

There is no regular sunnah prayer before the Jumu'ah (Friday) prayer. Rather, it is prescribed for whoever comes to the mosque to perform an absolute supererogatory prayer (nafl) as many rak'ahs as he wishes before the Khatib (preacher) ascends the minbar. As for the post-Jumu'ah sunnah prayer, two hadiths have been narrated concerning it: one mentions two rak'ahs, and the other mentions four rak'ahs. Scholars have differed on this matter, and there is latitude in the issue. The more accurate view is that whoever prays it in the mosque should pray four rak'ahs, and whoever prays it at home should pray two rak'ahs. This supererogatory prayer after Jumu'ah is a confirmed sunnah (sunnah mu'akkadah).