Grammar and spelling are a writer’s tools. Just as a plumber must understand and own a set of tools, writers must have a good grasp of grammar.
If grammar troubles you, I recommend reading Strunk and White’s Elements of Style. It’s a classic (and very short) book on using English well.
Once you get writing, ask another writer to read your work. Ask for feedback on your style as well as your content.
Practice writing and your grammar will soon improve.