I think you mean (CH2O)6, it is the formula for glucose (or it could be written C6H12O6).
The linear structure is characterized by the presence in the same molecule of a reducing function aldehyde or ketone and at least one alcohol function.
On the other hand, this linear form can be transformed into a cyclic form (in the solutions), and this implies the formation of hemiacetal by bonding between the aldehyde of carbon 1 and the alcohol of the penultimate carbon.
