Suffering, according to Christian tradition, is a way for mortals to test their faith in the divine. In Buddhist traditions, witnessing and experiencing suffering will lead to spiritual enlightenment.
For example, Saint Lawrence of Rome was slowly burned to death on the orders of Roman Emperor Valerian during the persecution of Christians. His suffering, according to Biblical stories, led to ecstasy. Witnesses smelled a fragrant scent rather than the charred remains of human flesh. His martyrdom led to his canonization as a saint.
Evil, as defined by the Abrahamic religions (e.g. Judaism, Christianity, and Islam), is the polar opposite of Good. In Christianity, the dualism of good and evil is mentioned throughout the New Testament. The Bible features various symbolism of good and evil: angels and demons; God and Satan/Lucifer; heaven and hell, et al.
Evil, according to secular Western Philosophy, is more broadly defined, and could be described as negative traits of the human psyche. In Western philosophical schools of thought, humans are capable of both good and evil deeds. Many literary and cinematic works explore the dualism of good and evil within a single character (e.g., the anti-hero).
Why is there suffering?
Suffering is an experience and a human emotion. There is no reason behind it or why it happens. Suffering is an emotional state that almost all humans experience in various levels and forms.
Why is there evil?
Evil, as a concept, is based on what we believe is moral. A person who doesn't abide by society's laws and social moral codes might believe that killing is not evil. The perception of evil is subjective. However, there are universal definitions of evil, such as rape and murder. Evil acts—such as terrorism or mass murder—happen due to various factors: politically-motivated actions; sociopathic and psychopathic behaviors; war; temporary insanity; bouts of anger; and so on.