http://www.uscga.edu/cadet2.aspx?id=419
Swab Summer - is swab summer. It includes a week on Eagle.
3rd Class Summer - two phases, 5 weeks aboard Eagle, 5-6 weeks assigned to a station or cutter. Responsibilities of a junior enlisted.
2nd Class Summer - mostly at CGA, ~2 weeks in Coastal Sail, T-boat training, cadre, CATP. Lots of cadets think this was their best summer
1st Class Summer - either 11 weeks assigned to a cutter as a JO, or half on a cutter and half at an internship.
That's it in a nutshell. Check out the cadet blogs on the CGA website to get a feel for what they experienced.