If a non-Muslim wants to convert to Islam does he need to choose between Shia or Sunni point of view at the time of conversion? Or is it just a matter of belief and he doesn't need to choose between that?
A non-Muslim who elects to convert to Islam, at the time of conversion, does need not to select between different sects, different schools of jurisprudence, or otherwise. The requirement to become a Muslim is to say Al-Shahadatayn (testimony of faith) in private or in public, which marks a person as entering the fold of Islam. It is preferred to perform ghusl (wash) then to pray two rak'as after the testimony of faith.
To continue being a Muslim afterwards, one has to uphold the five pillars of Islam:
- Al-Shahaadatayn (testimony of faith)
- Salah (prayers)
- Zakaah (financial dues)
- Sawm Ramadan (fasting the month of Ramadan)
- Hajj (pilgrimage)
There are numerous verses that enumerate the pillars. Here is a hadith that is quite well known:
بُنِيَ الإِسْلاَمُ عَلَى خَمْسٍ شَهَادَةِ أَنْ لاَ إِلَهَ إِلاَّ اللَّهُ وَأَنَّ مُحَمَّدًا رَسُولُ اللَّهِ، وَإِقَامِ الصَّلاَةِ، وَإِيتَاءِ الزَّكَاةِ، وَالْحَجِّ، وَصَوْمِ رَمَضَانَ
Islam is based on [the following] five [principles]: To testify that none has the right to be worshiped but Allah and Muhammad is Allah's Messenger (ﷺ), to offer the [compulsory congregational] prayers dutifully and perfectly, to pay Zakat [i.e. obligatory charity], to perform Hajj [i.e. Pilgrimage to Mecca], and to observe fast during the month of Ramadan.