Can you recommend any online resources, courses, or videos for learning simple furniture design and construction techniques, specifically in woodworking?

In my opinion the best resource to learn woodworking is wood. Acquire some, and do something with it. You don’t need to challenge the great furniture masters of all time with your piece. Make a box out of whatever you can afford. Even go so far as to use wood from the big box stores. Figure out from planning to trial and error how to make that box square. Figure out how to make a bottom and top for that box. In the woodworking specialty stores talk to the clerks, and ask them what you need to accomplish the task you have set. I visit woodcraft, and rockler stores, both near me. As you get your hands dirty, if you are going to stay in this hobby, you’ll figure out what you ‘need’.

BEFORE you saw, sand, or otherwise cut anything make sure you have adequate hearing protection, eye protection, and dust protection. Some of the plywoods are made with some nasty things you don’t want to atomize and then breathe. Some of the other woods may have other issues. Protect yourself! Protect anyone that comes into your ‘shop’. The goal at the end of the day is to leave the shop with the same number of lungs, fingers, toes, eyes, and ears that you started with. And maybe a head scratcher or two.

When you start to figure out what you need, look for sales, auctions, estates, friends, guys who loved it but have moved on to something else.

Don’t quit.