If you are staying at a hotel in Montreal, my suggestion would be to go to the front desk or concierge who can give you a map of the Metro system or go online before you leave. The system is colour coded depending on which area of the city you wish to visit. From each station stop, you can pick up specific buses (they are numbered) . Depending on how long you are visiting, you should look at getting a Metro Pass for 24hr, multi-day which gives you access to all public buses and subway trains.

best is to take the bus from Berri Uqam Metro ...just prepare in advance ,bok in advance Sherbrooke city is a small city

Public transportation is not available from Montreal to Québec it is a 4 hour bus ride ,only from the bus station on berri nowhere else, it's a set rate with no stop's. Greyhound is one ,I think there are buses that have discounted rates look online!!!

the bus for Quebec leaves at Berri Metro ..or even Longueuil (check Schedule) or the train at Bonaventure Metro...Buses are more frequent , the train has coach or first class with a fine meal with wine..trip time 2 hours by train , 3 hours by bus..7 day ahead booking can save ye 30%