How can a Muslim establish certainty in Allah and the Quran in their heart after being exposed to some doubts?

It is not permissible for a Muslim who is not armed with religious knowledge to visit websites that stir doubts and illusions. A Muslim must utilize their time and energy in seeking religious knowledge. They must also have certainty in Allah, the Hereafter, the word of monotheism, and the Quran, and remove doubt and suspicion from their heart, in affirmation of His (Allah's) saying: "Indeed, the believers are those who have believed in Allah and His Messenger and then doubt not but strive with their wealth and their lives in the cause of Allah. It is those who are the truthful" (Quran 49:15), and in condemnation of the hypocrites: "and their hearts have doubted, so in their doubt they waver" (Quran 9:45).