Graphing Hypothesis with uni variate linear regression • /r/MachineLearning

Hello, I've been following the machine learning videos on coursera with Andrew ng as the instructor. I don't know any math beyond a high school level so this is a bit tricky. I didn't understand how he was graphing this and what the H theta (x) meant when it came to graphing. I've searched on the internet a lot and couldn't find a video explaining what this means at all. If anyone would like to point me in the right direction that would be greatly appreciated.