It's difficult to properly advise without knowing where you will be based. Lake Comer See is a very large lake and there are numerous settlements all round its shores.
There are regular ferry and local bus services linking the numerous settlements around the lakeside.
I can't give you links to local bus services without knowing where you are based but you'll find ferry timetables and information in English on the official site:
Como itself has (several) railway stations from which you can easily take the train to Milan (don't miss exploring the magnificent Duomo roof!). Train times, details and fares in English on the official Italian railway website:
Ticket machines are easy to use and have English language options.
If you are based on the eastern side of the lake there's a railway line which runs up through Lecco and along the lakeside to e.g. Varenna. That line will also take you to lovely Bergamo, an ancient city with two parts (a Medieval upper town and a slightly more 'modern' lower town) which ismost definitely worth at least one full day of exploration. You can get to Bergamo by train from Como but it takes a bit longer and you need to change trains at Milan Centrale station.
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