What can they find out from a CT scan of your brain?

Many. Like stroke, bleeding, tumor, hydrocephalus, atrophy, some birth defect etc.
Obvious lesions. Cat is fast and helpful in er setting to rule out large intracranial masses or blood clots, and fractures of skull or sinus issues. Not so good for seeing early strokes, small lesions, such as ms, and subtle early secondary tumors.