What are Al-Qada' and Al-Qadar (Divine Decree and Predestination), and how can one resolve psychological problems and resist the whispers of Satan?

Qada' and Qadar (Divine Decree and Predestination) is what Allah destines and ordains, and everything occurs according to His decree and will, and there is no repelling His decree. Belief in Qadar entails believing in Allah's ancient knowledge, the inscription of that in the Preserved Tablet (Al-Lawh Al-Mahfuz), His pervasive will, and His creation of all creatures. It is not permissible to delve into Qadar, for it is a secret of Allah. Belief in Qadar does not contradict reliance on Allah (Tawakkul) and taking means, such as supplication (Du'a), psychotherapy, Ruqyah (Islamic exorcism/healing), associating with righteous people, and maintaining prayers and remembrances (Adhkar). Be keen on what benefits you, seek help from Allah, and do not despair. If something afflicts you, say: "Qaddara Allahu wa ma sha'a fa'al" (Allah has decreed, and what He willed, He did).