It is of paramount importance to be able to differentiate between various angiosperms in olympiads. Not only classification, but also anatomical structure is needed to know. So below you can find a brief introduction to monocots and dicots: http://biology.clc.us.edu/.
Take a look here at various plants cross sections.
Here you can find almost all major plant family floral formulas and more.
Image source: https://www.freepik.com/vectors/house-plant.