What would conditions on a high gravity planet actually be like?

I've seen conflicting accounts of how a planet with high gravity would actually work. That it would make flight harder to evolve vs easier, that it makes lifeforms shorter and slower vs taller and faster, that temperatures more stable vs more unpredictable, that weather would be more extreme vs less extreme. I really need help understanding what the actual conditions of higher gravity on a planet do to its environment and it's lifeforms.

Are there any easy-to-understand science based explanations of how conditions and life on high gravity planets might work for the purpose of speculative evolution?