There are many sources of help available to you as an undergraduate. Of course, one of your first sources of help should be your class deans who have a comprehensive advising system set-up.
Options for Help
You should see the Departmental Representative for your school (college, engineering, general studies) within the Physics Department.
The departmental representative will be happy to discuss with you any issues regarding a physics major, required courses, physics concentration, and any other academic matters.
If have questions involving a specific course, then you should speak with the professor teaching that course or their teaching assistant.
If you are having issues with a 1200, 1400, or 1600 lecture course, help from physics graduate students is available in the Physics Help Room (Pupin 413) Monday-Thursday 1PM-7PM and Friday 1PM-3PM.
If you are having issues with a 1200 or 1400 lab course, help from physics graduate students is available in the Lab Library (Pupin 506) Monday-Thursday 12PM-7PM.
There may be occasions when you have a matter to discuss and you feel uncomfortable talking directly with someone in the department. In these cases, you might be more comfortable talking privately with Columbia's Ombuds office.