glucose, as a solid, has five hydroxyl (OH) groups, and one aldehyde group (CHO) at the end in a linear structure. However, in the body glucose is generally found in a ring form as a alcohol. (see link below)
Aldehydes in general have the structure R-CHO where R is any carbon containing group attached to the carbon, and their is a double bond between the carbon and the oxygen. Ketones are similar but their general structure is RCOR' , where both R and R' are carbon containing groups, and there is a double bond between the carbon and the oxygen.