Aside from exploratory qualitative research, most research comes down to examining relationships among theoretical constructs by measuring variables that correspond to those constructs and looking at statistical correlations among the variables.
Sometimes the correspondence between the theoretical constructs and the operational variables is quite close. For example, if you are looking at how humans gain weight as they get older, you have a construct called Age, and another called Weight. These are operationalized by recording the number of years that have passed since that each person was born, and measuring their weight in pounds on a scale.
Sometimes the correspondence is more tenuous. For example, you might have a theory that the performance of a top management team is a function of their ability to communicate with each other. Performance can be measured by profitability. But you may be unable or unwilling to try to measure their capacity for communication. Instead, you measure the number of years that they have worked together, on the assumption that over time they learn to read and understand each other, so they communicate better. So to test the theory, you correlate profitability with number of years worked together.