Because you said your timetable has a conflict. That means you are enrolled in two classes that are happening at the exact same time. Since you can't be in both places at once, you need to change your timetable to be conflict-free.
This is the time table generator that was mentioned by a previous poster:
http://www.timetablegenerato r.com/
Also, as that poster said, you'll search the course code in the master timetable, and click the link for the course in the page that follows. That should open a new window, which will tell you the day and time of the course, the location of it, and the professor teaching it (exceptions being labs and tutorials, which are handled by T.A.'s).
In the timetable generator, enter the course and its core/tutorial/lab you want to be enrolled in. It'll add it to the timetable. Keep doing this for all the courses you have, and if a conflict occurs, change the conflicting core/tutorial/lab to another one until you have a full conflict-free schedule.
Now, that being said, on Thursday you will have to go into SOLAR and "Modify" the courses to match the schedule that you've made in the time table generator. Once you've applied the changes you can check the timetable on MUGSI and make sure there aren't any conflicts.
Often, I remake the schedule that Mac gives me regardless because I like to compact all my class into the morning and be finished earlier in the day (gives you a big headstart on homework and studying). I remember that being hard to do in first year Engineering though.
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