The INDIRECT function in Excel allows you to reference cells by typing the cell position (for instance: "B2"). To clarify this, look at the first example, you can see in the function bar that it's a direct reference.
In the following example, the indirect function is used with the parameter "D3" as text and brings the same result.
Now, as the parameter of the indirect function is text, you can concatenate and build the cell reference by using other cells.
It's clear that using a direct reference (example 1) is better than using the indirect function, however, there are cases where is required to build functions dynamically depending on other values and the indirect function is a great tool to consider for these situations.