Currently life on planet Earth is divided into five (5) major kingdoms; six (6) if you split Monera and seven (7) if you add viruses. These kingdomes are the top most category of the current classification scheme and contain organisms that are loosely related. In other words, grass and trees are together and elephants and crickets are together, and mushrooms and mold are together. You'll remember that as we go from Kingdom to species, the number of organisms decreases and the relatedness increases!
Animal Kingdom: These organisms are multicellular, heterotrophic (they have to go and get their food), have a nucleus (eukaryotes), and are relatively complicated.
Plant Kingdom: These organisms are multicellular, autotrophic (they can make their own food through photosynthesis), have a nucleus (eukaryotes), and are relatively complicated with both a cell wall AND chloroplasts.
Fungi Kingdom: These organisms are multicellular, heterotrophic (they have to get their food), have a nucleus (eukaryotes), somewhat complicated with a cell wall but no chloroplasts.
Protists Kingdom: These organims are single celled, can be heterotrophic OR autotrophic, have a nucleus (eukaryotes), are a complicated cell with both animal and plant cells among the various species of protista.
Moneran Kingdom: These organisms are single celled, heterotrophic, NO nucleus (prokaryotes), very simple cells. Monerans are mostly bacteria but, in many cases viruses are thrown in here because they really don't fit anywhere else!
Eubacteria: These monerans are very common to humans. They are found everywhere and are mostly beneficial, can make us sick, or don't really do anything bad- to us! Some (about 5% or so) are very deadly and will kill us.
Archaebacteria: These monerans are found in "weird" places- like the boiling hot springs in Yellowstone, miles under the ice in the Arctic, up high near the outer limits of our atmosphere, etc. They are not common.
Viruses: Viruses are casings of protein surrounding viral DNA or RNA. In order to reproduce more viruses, a virus MUST infect a cell and USE that cell's mechanisms (ribosomes) to create more and more viruses. There is still debate over whether a virus is considered alive or nonliving because without a living cell, a virus cannot fulfill all the 8 life characteristics!