The three different variables in science are independent, dependent, and controlled. The independent is what you change in an experiment to have a different result. The dependent is the variable that depends on the change in the independent. The control is the variable that does not change in the experiment.
The image above shows the scientific method. It helps a scientist figure out a question or what he/she is wondering about.
Here is the 5 senses. You have sound, smell, taste, touch, and sight. You use these to make qualitative observations. The senses are very important to the scientific method.
A quantitative observation is an observation of measurement. The measurement can be height, weight, volume, ect.
Qualitative observations are descriptive observation on sights and how they feel, smell, sound and sometimes, how it tastes.
An inference is basically coming to a conclusion from your observation. So this is important to your observation.