Inorganic substances are:
small and simply built
consist of only a few atomic types
main examples: O2, CO2, H2O, NO3, N2 etc.
Organic substances are:
more complicated in construction
consist at least of C, H and (usually) O atoms (often N and / or P and sometimes S and other types)
are produced by organisms
main examples: glucose, starch, amino acids, proteins, DNA / RNA, chlorophyll