Free Basic Science Websites?

I'm an 8th grader, and I'm in a Science Honors cl, I have NO idea why! I barely understand science at all, out of 45 question in a test I'll probably get 15 right that's how bad I am in science. I'm from Venezuela and came to USA when I was in 4th, I don't know if the learning is different or something but everything that they now explain in cl I don't recall learning. I'm freaking out because I might fail a major test, if I don't learn at least the basics on science fast! So are there any websites that have free lessons, videos, and activities to help me learn? Thanks.