The Physics Classroom and Khan Academy both have excellent free on-line courses on physics, starting from the beginning. They’re step-by-step and give practice problems. On Khan Academy, if you sign in, it will keep track of your progress. It also gives “awards” like badges for good progress. Both websites are excellent. Khan Academy is a little more interactive. I have used both. To really gain understanding and certainty, I’ve done lessons on the same subject on both websites.
When I didn’t understand something in a particular lesson, I found videos on Youtube. I typed the subject into the Youtube search bar, for example, “inertia.” Then, I just started watching videos until I finally got it.
It’s important to understand all the jargon as it comes up. When terms came up I wasn’t sure of, like “mass,” I watched Youtube videos on the subject and/or googled the physics meaning. When googling, I often asked for images. Finding visuals really helps.
I’m writing definitions of physics terms in an on-line encyclopedia. It focuses on quantum physics, but many of the terms, like acceleration, are shared with classical physics. Classical physics is the first physics that you learn on websites like the PhysicsClassroom and KhanAcademy.org.