There are several ways to begin the quest to identify your "unknown" car. Look for a firewall tag or cowl tag. These usually indicate the Manufacturer and sometimes even the year of manufacture.
The shape of the rear window is sometimes a good indicator at least of manufacturer, though not necessarily the make.
Do the door open from the rear or from the front(suicides).
Is the body structure mostly wood or steel using wood around the window openings and the top hole?
Does the car have a cowl vent or two?
Does the windshield tilt out for ventilation or roll up?
Is the suspension dual leaf springs at the front and rear?
Are the brakes hydraulic? All Chrysler products from 24-up have hydraulic brakes. GM started in 1936. Ford started in 1939.
Get a copy of the The Old Cars Weekly Auto Identification book printed in Iola, WI.