In an experiment, the variable refers to something that changes in an experiment... This can be anything, it's a matter of controlling/changing it per your needs... here:
Dependent variable: You measure this in an experiment. The dependent variable's results are influenced by the independent variable - e.g., the rate of growth of a plant would be influenced by how much water you add. - see below
Independent variable: This is what is intentionally changed in an experiment. You change it in order to achieve the results/observations you want. Adding different amounts of water (independent) to a plant to see the rate of growth (dependent - it depends on the amount of water.)
Controlled variables - you keep this the same in an experiment to make sure it is not influencing your results... E.g., making sure the amount of sunlight provided is constant on the plant/plants
Experimental Control - used to make an experiment valid. To prove that your independent variable was actually influencing your results. A control would be a plant that has no water added to it, so you can see the effect of different amoutns of water on a plant, by comparing to the plant that had no water.
Other skills - I can bet you will be tested on reading diff. types of graphs (e.g, bar , pie, column, line) and interpreting data from tables.
these are off the top of my head.. so if anyone has any corrections, please feel free