Iam sorry but i have to ask 
Do you know how to use google? You ask sometimes pretty simple questions that usually can be answered with just a short search on google :)  

If you google 
you will see there are several trains from Milan to Como 
From a Regionaltrain up to a Eurocity. How to book depends if you are on Interrail or not? With Interrail you just fill your travel diary and catch a Regionaltrain. To find the depature times i recommend to have a look on the Website of Trenitalia or TreNord. 

Kind Regards and a Happy new Year  

In my opinion Como is not the best place on Lake Como. Do some research based on what you like to do. Then look at a map and decide. There is a railway that runs up the Eastern side of the lake linking the town and villages with direct trains to Milan.