you need to understand the change in the models for gravity throughout history. Starting with Newton (although I don't necessarily think he is the first one to think or mention it; maybe 'English' history is just going to credit 'English' scientists, but he was a badass either way); then when you have to account for the speed of light, you need to understand that this entailed more than just 'that', there is a re-conceptualization of space involved as well -- Einstein had to float around getting help from mathematics professors and colleagues for years to get the tensors together

Then you need to understand what it actually means when applying it to the real world or other branches of physics; for example, if light bends around massive objects, but gravity is a force, then how can a 'force' be affecting the trajectory of another force? If you decide that gravity isn't a 'force', but instead just geodesics of space-time curvature, then why is it treated mathematically as a force? That last one is still a question being asked by physicists today, by the way - although they usually realize that the equation is just an equation, and when they need to they are able to account for the inconsistencies using common sense.