When are you visiting?
The main transport option from the Calgary area to Banff/Lake Louise are airport shuttles. I believe that Brewsters/Pursuit also runs a shuttle from some downtown hotels, though with limited timings. There are a few day tours from Calgary, though most tend to be based out of Banff.
On weekends in the summer, there is also a bus service that departs from a couple of the C-Train stations in Calgary. It's more focused on locals, so the stations are at the north and south ends of town. You could take the C-Train from downtown to the stations. I think it's $10 one way.
Whether/if any of these options makes sense for your needs depends on when you are visiting, where you are staying in Calgary and where you want to go in the mountains. Most of these options are only available late May to early October. Outwith that time, airport shuttles and a rental car are about the only realistic options.
Also, if you want to go Lake Louise, there are buses in the summer, though the transfers can quickly eat into the time you have to see and do things. There are no buses, other than Greyhound, which has a limited and inconvenient schedule.
You can take the On-It Regional Transit bus on Saturday (cheapest option for a day trip - $20 round trip plus $~10 for a park pass for the day); if interested, buy your tickets online ASAP:
For more money, you can catch the Brewster / Pursuit bus downtown tomorrow or Saturday:
Thank you so much. I'll look into it