Sadly, many students get the idea that grammar is “too hard” for “ordinary” people to learn. That’s a mistaken idea that comes from trying to cover too much material too fast.
An English speaker who has mastered the Parts of Speech and the Parts of the Sentence will be able to produce error-free speech and writing. The key to mastery is putting in the work to learn them.
Take one grammar concept at a time. When you understand it completely, go on to the next one. Practice makes perfect.