I asked a similar question about Luzern recently....if you could only spend 3-4 hours in Zurich in an afternoon, and had to start and end at the train station, where would you choose to go by foot in that period of time?
I would go to a nearby cafe and sit and read my book.
You can walk out of the main train station on Bahnhofstrasse all the way to the lake. Do some window shopping along the way and know that most of the world's refined gold sits in vaults under your feet. At the lake take a left and head to the old town (Atlstadt) and meander through and wind around back to the train station.
Not especially creative, but what I did do with both an afternoon and evening in Zurich was first to visit the Swiss National Museum (near the train station and covered by an active Swiss Travel Pass) and later walk to the lakefront before finding dinner.
Are you vegetarian/vegan? The oldest vegetarian restaurant in the world, Hiltl, is in Zurich. We are planning to stay 2 days but that's on my not-to-be-missed list.
I enjoyed the Museum next to the train station, but it can take up lots of your time, and you will miss the "feel" of Zurich, a lovely city. If you don't want to do the museum, you could easily walk to the Fraumunster Church to see the Chagall windows, then continue down towards the lake on Bahnhofstrasse. If it is a nice day, I would walk down to the lake and take a boat ride. Very scenic, and I think a ride was just an hour long. You could then take the trolly back up Bahnhofstrasse, over the river, and walk around the historic Niederdorfstrasse area, which is close to the train station.