Since there seem to be a bajillion posts all asking the same thing about editing your timetable, I'm going to post it here.
You can edit your timetable on SOLAR. If you are fully registered
(ie, confirmed your payment agreement by Aug 10), and have all outstanding fees cleared
you may access SOLAR starting Aug 11 at 8:30am EST. Outstanding fees do not
include tuition. Tuition isn't due until Sept 1, therefore it isn't outstanding. Outstanding fees are past their due date (example: summer school tuition).
You can edit your timetable for BOTH terms starting Aug 11. You can also drop/add courses, but it will be your responsibility to select your sections. If a course is available, but the only sections that aren't full conflict with something else you have, then either try to change the other course or email the prof/IA for those courses to see if they can switch you. Often, there is an opportunity to do that at the beginning of each term as well.
If you would like to pick your section based on which prof teaches which section, you can view the profs for each section on the master timetable: https://adweb.cis.mcmaster.ca /mtt/
If the prof you want teaches C02, then you'd have to select C02 on SOLAR (provided that C02 doesn't conflict with any of your other courses, and that it isn't already full).
EOW = every other week. If you're in chem, you must have the same lab/tutorial section numbers, because one week you have the lab and on the 'off' week you'll have a tutorial in the same timeslot.
The Drop/Add deadline for Term 1 and 3 courses is September 17th
The Drop/Add deadline for Term 2 courses is January 11th.