Ok, so, to get around in the city, if you don’t know how, a good trick is to remember A-U-T-O-B-U-S (288-6287) the phone number of the STM, they will tell you the best way to reach your destination by using public transit. And a monthly bus pass is $54.
As for getting acquainted with the Metro,matt_mcl should be the one to answer. But I will do what I can. There are 4 metro lines :1 (east-west), 2 (north-south), 4 (south) and 5 (east-west). It’s not as complicated as it sounds. Line 1 or Green line is basically east-west at the downtown level, while line 5 or Blue line is east-west at about the middle of the island. Line 4 or Yellow line goes across the St-Laurent river, you use it to go to the Casino, La Ronde or Longueuil. Line 2 or Orange line goes from Ahuntsic (north-east) to downtown (Bonaventure station also the train stations are located there), to Côte-Vertu (ville St-Laurent, north-west). There are also three transfer stations, if you want to change line : Berri-UQAM (transfer to the green, orange and yellow lines), Lionel-Groulx (transfer green and orange lines) and Snowdon (transfer orange and blue lines).
As for interesting location, You might want to check the Atwater market for fresh foods.
scott evil and matt_mcl would probably be your best guides for the Gay village.
If you’re a party girl, Bishop or Crescent street, St-Laurent boul. (above Sherbrooke) or St-Denis street would probably be your best bets. Also, remember, in Québec, beer and wine are available in grocery store and dépanneurs (convenience stores) and they deliver.
St-Laurent boul. is also more than bars. Nicknamed the Main, it is the dividing street in Montréal, between east and west, it also contains an almost infinite quantities of small, ethnic, mom and pop stores.
For more mainstream shopping, Ste-Catherine is the street for it.
For more exotic shopping, St-Denis street, above Sherbrooke, is the one to go for.
For upscale shopping, Laurier, west of Park is recommended.
I hope these infos will provide useful.
Oh, one more thing, here are a few useful maps including one for the metro system.