Alright, so, if you’re going to start teaching yourself you gotta keep something in mind.
Grammar, and sentence structure are two entirely different things (I’m not an expert here, so let me just tell you what I learned and what I remember).
What’s confusing you is most likely ‘sentence structure’ in the sense of how objects are signed followed by their descriptors. In that sense I would wait until your actual course to learn that from your instructor because if you learn wrong, you’ll spend months trying to rewire your brain and that can get exhausting.
The grammar in ASL is all in the eyebrows. Raised brows and wide eyes are for yes/no questions, and furrowed brows and narrowed eyes are for your wh/how questions. Mix them up and people will be like….huh?
It’s okay to learn some signs and commit them to memory. It will definitely help you to recognize stuff if you want, but honestly, starting the course from scratch is a lot of fun.
Now what I would recommend, and what you can get a head start on, is fingerspelling. That shit is haaaaaaard. Memorize the alphabet, and then work on your transitions. Fingerspelling will get you out of so many binds when you forget a sign, and for names and stuff.
So if you want to learn some signs, absolutely. Go for it. I just wouldn’t try to put them into phrases yet because that’s where things can get a little confusing. Focus on fingerspelling instead.