A whole life in one cell
Some organisms live an entire life as a single cell. They are the unicellular organisms.
Look at the structure of one and what you find is cytoplasm and the organelles it holds, surrounded by a plasma membrane. Yet everything an organism needs happens inside that one cell — nutrition, respiration, excretion, movement, reproduction.
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You can see this yourself
Examine a sample of pond water, or a hay infusion, under a light microscope. Unicellular organisms are easy to observe. Identify the ones you find and draw them.
There is organization inside one cell too
"Unicellular" does not mean "simple". Paramecium has cilia for moving, an opening for taking food, and contractile vacuoles for pushing water out. A unicellular organism has organization at the organelle level.
Why this is the first characteristic
That single-celled state is itself an organism, and it is what expresses the characteristics of living things. A stone has no cell; a piece of glass has no cell. Having a cell is what sets the stage for the other seven characteristics.