It may sound boring but just study horses. The ones making hurr-durr and snorting. They are the base as I call it. Then shape your “horses” into cartoon “ponies” as much as you find attractive. Start with skeletons and and learn main bones and muscles. It’s called plastic anatomy.
And yeah, he is right about cylinders. The whole horse body is a large sausage. At this point everything is about how often you practice.