Ferry schedule depends on the months of the year; so make sure to look at the correct schedule for the month you are visiting.
* March - May
* June - November
This is ferry operator NAVIGAZIONE LAGO DI COMO schedule homepage: https://www.navigazionelaghi.it/en/
Here is the current 2024 March-May weekday schedule:
https://www.navigazionelaghi.it/wp-content/uploads/2024/03/05P2024_Web_TrFeriale.pdf
Check back later for the June-November schedule.
There are various ferry routes, the mid-lake route Corse Traghetto operates only in the central area of Lake Como (Varenna, Bellagio, Menaggio, Cadenabbia); so this is the one you want to take. It’s mostly car ferries but also a few fast ferries (passengers only). Fast ferry has no outside seating; so on a sunny day you might want to take the car ferry to enjoy the view from the deck. The car ferry piers are marked by the word "Traghetto”; a seperate pier serves passenger-only fast ferries. These two types of ferry piers are close to each other at Varenna; but are on the opposite sides at Bellagio. So make sure to go to the right version of pier you want.
On www.navigazionelaghi.it/en/ ticket website select 'Lake Como'; there are two pier options with similar name:
For Varenna: Varenna & Varenna (Traghetto)
For Bellagio: Bellagio & Bellagio (Traghetto)
Select Varenna (Traghetto) & Bellagio (Traghetto) if you want to take car ferry (more frequent ferry services).
You can buy the ticket at the ferry pier or onboard the ferry. But during busy season the ticket line can be long; that happened to me when I was there last year. Luckily I was able to bypass the ticket line by buying it on their website; and went straight to the boarding line. You can go to Navigazione Laghi website or use their mobile app called 'DreamLake' to buy your ticket.
If you are traveling between Como (left southern tip of the lake) and Bellagio; you will take the fast ferry (the only option). They don’t sell the ticket for this route online, so you will want to show up early to buy ticket as during the busy season the line can be long and tickets can sold out. This particular fast ferry route runs not very frequently (see schedule); if you miss it you will have to wait a long time for the next one.
P.S. I rode the Treno (https://www.trenord.it/en/) regional train from Milano Centrale to Varenna Esino; and the ferry pier is walking distance from the train station. https://goo.gl/maps/PjiT7MzZyYutBXvi9
Have a wonderful trip!