How do MIT OpenCourseware and real MIT courses compare? Are MIT courses much different from MIT OpenCourseWare? I am curious, because as a high schooler, I have some intent to study from MIT OpenCourseWare.

Will this allow me to be more comfortable if I am admitted to MIT?

Also, how are MIT courses so different from those at other places? I heard that these courses are hard..
MIT OCW doesn't offer "courses".  It offers "courseware" — basically textbooks with videos.

Real MIT courses have live instructional staff who answer questions, run recitation sections, and offer feedback (in particular, grades) on your solutions to the homework and exam problems.  Real MIT courses have deadlines that force (well, encourage) you to actually work on the course material regularly.  Real MIT courses also have a community of other students, all following the same lock-step schedule, that can work together to develop ideas, internal feedback, social outlets, and later professional contacts.  Real MIT courses give you an official record from MIT of your performance in the class.