Rule 1: 1. Naming the day
Each day is an iḍāfa: يَوْمُ plus a definite noun. On Friday is simply the accusative يَوْمَ الْجُمُعَةِ or فِي يَوْمِ الْجُمُعَةِ. In speech the word يَوْمُ is often dropped: اَلْجُمُعَةُ Friday. The week is أُسْبُوعٌ, plural أَسَابِيعُ.
فِي الْأُسْبُوعِ سَبْعَةُ أَيَّامٍ، أَوَّلُهَا يَوْمُ الْأَحَدِ.
fi-l-usbūʿi sabʿatu ayyāmin, awwaluhā yawmu-l-aḥadi
In the week there are seven days, the first of them being Sunday.
يَذْهَبُ الْمُسْلِمُونَ إِلَى الْمَسْجِدِ يَوْمَ الْجُمُعَةِ.
yadhhabu-l-muslimūna ila-l-masjidi yawma-l-jumuʿati
The Muslims go to the mosque on Friday.
Accusative of time: يَوْمَ.
زَارَنَا عَمِّي يَوْمَ الِاثْنَيْنِ وَسَافَرَ يَوْمَ الْخَمِيسِ.
zāranā ʿammī yawma-l-ithnayni wa-sāfara yawma-l-khamīsi
My uncle visited us on Monday and travelled on Thursday.