I would take a train to Varenna/ Esino Station. I would be undecided about my return route.
In Varenna/Esinio, I would walk down to the ferry dock. I would go to the south end of the ferry parking lot and walk along the lake front promenade then up one of the stair streets to central Varenna. Total time needed in Varenna (Half hour to 60 minutes. It is small but many say a typical small italian town.) Varenna is heavily influenced by its history as a fishing village. ( I would take some photos).

I would take a boat (probably a car ferry) to Menaggio. I would walk Menaggio's lake front road and promenande (this is a roman road, altho' it does not look it). I would find Menaggio's pedestrian only area (Where the tourist shops are, if they are open). Menaggio is the intersection of the roman road and the road to Switzerland, so it feels different than Varenna). I would take some photos.

I would go to Bellagio. At Bellagio decide if you want a long boat ride (south to Como) or not. In addition to the lakefront (which is longer than many on Lake Como), I would walk up at least one stairs/streets up to the ridge. Bellagio is at the end of a peninsula. Bellagio is mostly about tourism. Take photos.

At this point, you either take the boat down to Como or back to Varenna.

Bellano is just north of Varenna and a nice place to visit. But no Train service and less frequent boat service.
For a day trip, timing would be very important.

The lakefront promenades can provided great photos. Every town that we visited has one (but I have not seen every town on Lake Como). The best views have the lake, mountains, and maybe some buildings. You can preview the experience by looking at other people's photos. (Click on my name above and look for a posting on a professional photographer.) The mountains that ring the lake range from several thousand feet high to about a mile high (so I can't think of anywhere that there are not views.) From Bellagio, look direct across the lake, sight about half way up the mountain there is a small chapel (half way up one heck of a mountain. 2,000 feet DOWN to get to any other structure.)

Have a good trip. Take a good camera and plenty of film. Beautiful.

Villa visiting is also popular. Villa Carlotta has been recommended. It is in a town south of Menaggio. Don't know what villas will be open in February.

Thank you so much for such a detailed and helpful reply, Doble!