Is there a list of disbeliever and shirk acts, and do you have to say the Shahada again, if you do them? Or is there a website which lists them? In a article?
Shirk is the violation of Tawheed (oneness and Uniqueness of Allah swt.)
Shirk in al-Rububiyah - Believing that there is another that shares in the Lordship of Allah swt
- Associating partners
- Negating the Lordship of Allah swt
Shirk in al-Asma was Sifat
- Humanizing Allah swt
- Deifying Human beings
Shirk in al-Ibadah - Directing worship to other than Allah swt
Taghut (worshiping something along with Allah swt or instead of Allah swt). This is Major Shirk or Ash-shirk Al-Akbar
ar-Riya (showing off) ie. Doing acts of Ibadah not for the sake Allah swt but for the sake of others. This is minor shirk or Ash-shirk al-Asghar
Many things, including, neglecting salat can make you kafir.
“Between a man and shirk and kufr there stands his neglect of the prayer.” (Narrated by Muslim in Kitaab al-Imaan from Jaabir ibn ‘Abd-Allaah from the Prophet saw).
The most important act of kufr being denying Allah and his Prophet salah allahu alayhi wa salam.
As far as coming back to Islam after shirk or kufr if you return to salat and ask for forgiveness this should be sufficient if Allah swt wills. As Allah swt says:
فَإِن تَابُواْ وَأَقَامُواْ ٱلصَّلَوٰةَ وَءَاتَوُاْ ٱلزَّڪَوٰةَ فَإِخۡوَٲنُكُمۡ فِى ٱلدِّينِۗ وَنُفَصِّلُ ٱلۡأَيَـٰتِ لِقَوۡمٍ۬ يَعۡلَمُونَ
But if they repent and establish worship and pay the poor-due, then are they your brethren in religion. We detail Our revelations for a people who have knowledge.