You can take your bicycle with you on most Suburban, Regional, Direct and Inter-regional trains in Italy. Look for the bicycle symbol in the timetable.
Sometimes they have special offers allowing you to take your bicycle for free on certain lines and certain dates (look for the posters at stations, in bicycle shops and at the Ciclobby office in Milan), but in general you have to buy an extra ticket for your bicycle. This costs EUR 3,50 and is valid for 24 hours from the time you have validated it by sticking it into the yellow "Convalida" machine at the station.
Your own ticket is only valid for six hours, but the idea is that if you are making two or more trips within 24 hours you can use the same bicycle ticket for both or all of them.
These bicycle tickets are not available through the blue ticket machines, so to get one you have to go to a ticket window and buy one from a real person, which in my experience is no problem and doesn't take very long. (No guarantee on that, however! I didn't try it during the rush hours.)
If by any chance you are going on a short train trip that costs less than EUR 3,50 to begin with, and you know you only want to take your bike with you on that one trip, you can simply buy a second ticket for your bicycle for the same price as yours (from the ticket machine, for instance), but in that case both tickets, yours and the bicycle's will only be valid for six hours from the time you have validated them.
The first photo shows the 12:15 train to Mantova, on track 21 of Milan Central Station. This is the train I took to Cremona with a bicycle I had rented in Milan.
Second photo: Don't forget to validate your ticket -- and your bicycle ticket -- before boarding the train. You do that by inserting the tickets, one at a time, into one of these yellow "Convalida" machines.
Third photo: The regional and local trains in Italy have these bicycle transport carriages at the opposite end of the train from the locomotive. As in Germany, it is not always easy to find out in advance which end of the train that will be, but on the Milan-Mantova line, via Cremona, the locomotive always seems to be pointing towards Milan, so the bicycle carriage is at the front of the train going from Milan, and at the back of the train going to Milan. Okay?
Fourth photo: If lots of people want to transport bicycles at once, it is possible to hang them up on these hooks to save space.
Fifth photo: Here's a poster advertising one of those special offers: free bicycle transport on certain trains on National Bicycle Day.
There are seven direct trains per day from Milano Centrale (Milan Central Station) to Cremona, and three from the station Milano Porta Garibaldi.
My train took an hour and ten minutes from Milano Centrale to Cremona, stopping at several stations along the way including one with the marvelous name of Casalpusterlengo.
In Cremona you could theoretically change to a local train going to Busseto, but I didn't do that because I went to Busseto by bicycle.
From Cremona there are railroad lines going off in five different directions:
•North to Brescia
•East to Mantova
•Southeast to Parma with stops at Busseto and Fidenza
•Southwest to Piacenza
•Northwest to Milano