As a mental health therapist, I have to disagree that schizophrenia is an umbrella for many serious mental health diagnses. This may be the case in error. According to our diagnositic manual, schizophrenia has many types, like paranoid type, disorganized type, and catatonic type. Characteristic symptoms include things like delusions, hallucinations, disorganized speech, grossly disorganized or catatonic behavior, or flat affect (basically no emotion). There is evident impairment in functioning in many areas including social, work, or self care.
I often see patients with paranoia. Many people who present for treatment for schizophrenia think they are being controlled. They think they are being watched or people are talking about them. There are commonly auditory or visual hallucinations. Many believe they are being told to do things, but visual hallucinations often involve seeing things in their periphery.
Age of onset is typically in late teens and early twenties, but people who will eventually receive this diagnosis have often shown symptoms before this. Schizophrenia appears to be genetic. Many, many twin studies have been conducted and whether raised together or apart (adopted) it is much more likely for both twins to be diagnosed with schizophrenia than only one regardless of their environment. There are medications that can help control the symptoms of schizophrenia, antipsychotics, like zyprexa, Seroquel, and Risperdal. These medications, when found in the right dose and combination for a particular patient (remember brain chemistry is very different in each person) can lead to a person looking at the world more rationally and often leading a more "normal" life.
Hope this helps!!