Lessons for someone starting work for the first time in United States

I am graduating December and starting work as a software engineer. This is my first job in the United States. I am very scared about the cultural difference in addition to all other first job fears.

Any tips, advice or lessons that you learned in the workplace would be very very helpful.

For example, should I get some chocolates for my coworkers in the first day? I remember seeing someone do this when I was an intern.

Please help.