Can someone please explain to me in simple words the process of calculation to measure the size and the distance of a star (or a galaxy for that matter)? What are the measured values? I have read about what I think could be two "relatively easy" measurable variables such as “apparent size” and brightness. Still, it is not clear to me how to differentiate a very bright and distant star from a dim and near one. Also, I have no idea about how the size on the object can be calculated.