You can really feel the difference between the two. The iPhone 12 is lighter and not as dense. The difference in weight is mainly because of their materials. The iPhone 12's flat edge frame is made of aluminum, whereas the iPhone 12 Pro's body is "surgical-grade" stainless steel. Aluminum is substantially lighter.
Why should you care that the iPhone 12 has 4GB of RAM and the iPhone 12 Pro has 6GB of RAM? A few reasons, actually: more RAM usually means better OS responsiveness (especially when you have tons of apps open), more efficient processing, and – this one is important — more runway for future software updates.
Still not sure if you should get an iPhone 12 or 12 Pro? Check out our in-depth review, where you'll find tons of camera comparisons between the iPhone 12, 12 Pro, 11 Pro, and Pixel 5.