I have heard some people said that sunnat prayers are a must after each/after each salah. What is the ruling about reading sunnat and why people says that reading Jummah (friday prayer) Sunnat and Maghrib is a must?
Sunnah prayers are important because they make up for any deficiencies in the Fard prayers we offer. Sunnah prayers are broken down into two categories. The first are the Sunnah Muakkadah (high emphasis). Since the Prophet (ﷺ) consistently used to perform the Sunnah Muakkadah prayers (and never left them without reason), Muslims should also regularly perform these. These include Sunnahs of Fajr, Maghrib, etc. The second are Sunnah Ghair Muakkadah (no emphasis). There's no blame if these are skipped, because the Prophet (ﷺ) at times did not offer these. Below is a convenient list of prayer classifications (source).
Fajr: 2 Sunnah [Muakkadah], 2 Fard
Zuhr: 4 Sunnah [Muakkadah], 4 Fard, 2 Sunnah [Muakkadah], 2 Nafl
Asr: 4 Sunnah [Ghair Muakkadah], 4 Fard
Maghrib: 3 Fard, 2 Sunnah [Muakkadah], 2 Nafl
Isha:4 Sunnah [Ghair Muakkadah], 4 Fard, 2 Sunnah [Muakkadah], 2 Nafl, 3 Witr, 2 Nafl
Let me know if you have any further questions.
السلام عليكم ورحمة الله وبركاته