You have arrived here because you have a question that involves the likelihood of a particular outcome for a patient with a certain disease, condition or injury. It may also involve identifying risk factors for an outcome amongst patients with a certain disease, condition or injury.
For example, how likely is a kid with a febrile seizures to actually develop a seizure disorder; how often do people with tibia fractures have non-unions; what risk factors increase mortality in patients with acute myocardial infarction.
The first step is to map out your prognosis question (the purpose of mapping a question is to facilitate a literature search). You must think about three things, Patient population, Intervention, and Outcome (P.I.O.). Actually, what might help is for you to think about this as if you were actually designing a study.
Patient population- What population are you interested in? Is it patients in an emergency department, patients referred to a specialist, etc. What demographics like age, sex, race, are important. Do you want patients with a certain condition (i.e. asthma, or diabetes).
Intervention - With this type of question, the intervention is usually TIME. You usually don't do anything, you just observe to see if something occurs over time.
Outcome - Are you interested in mortality, morbidity, admissions to hospital, prolonged recovery, increased medical needs, etc.