The two most iconic villages on the Lake of Como are for sure Bellagio and Varenna.
You can get there with public bus, but the best way is for sure by the lake. There are fast ferries leaving Como City Center in the morning and coming back in the afternoon.
In Bellagio you can easily spend a couple of hours walking through the narrow streets or going up and down on the steps which pass through the houses.
Before or after lunch, go by boat to Varenna and spend a couple of hour also there, walking “on the lake” on the passages full of flowers.
These small towns are really small and you can’t get lost. However, if you have more time or if you arrive there by motorbike and you have more flexibility, consider the possibility to visit Villa Melzi in Bellagio or to go up to Vezio Tower over Varenna; there, you can also find a statue which looks like an Harry Potter’s dementor.