The Emmanuel College website lists directions to the College by bus, train, bike and air on their website.
The University provides a street map of Cambridge, available here, that shows all the Colleges and Departments of the University.
When you arrive at Emmanuel you should enter the College through the front entrance on St Andrew's Street. Immediately inside the entrance, on the right, is the Porters' Lodge which is manned 24 hours a day.
The College hosts numerous Open Days for prospective students throughout the year. For more information visit this page. You should contact the Admissions Office if you want more information or want to arrange a visit on a separate occasion.
While visiting a few colleges will certainly help you to make up your mind as to which to choose, it's by no means essential. If you can't make it in person, you might like to view the online tour of Emma.