Hello~
1) You can sign up for an online course on SOLAR, it's just like signing up for any other course.
2) How it works is every week your Prof will post a lecture(s) online on Avenue and you can access them at anytime. Night, morning, afternoon, anytime! Which is awesome and you can replay the lectures as many times as you want.
3) The only time you would have to go to school in person for this class would either be if you have tutorial or your Prof will tell you if the class meets up on certain days. I took 1DD3 last and even though it wasn't an online course we didn't have tutorials so I'm guess this year you won't have them either-double check the course outline though.
Hope this helps!