Here is the deal on travel pay: It's complicated.
Cadets get Comrats automatically without submitting paperwork for school leave periods, ie: Christmas and Thanksgiving like
@Sierra describes.
For summer duty travel, Cadets do an E2 online trip authorization form before they go requesting funds. USCGA pays travel from Academy to duty station and back to Academy. However, you can take leave in route to visit home, etc. You have to do a constructed cost request before travel to do this. What it basically means is the USCGA will pay up to the cost of what they would pay to get you back from your assignment and not more, they call that "most advantageous to the government." If you want to do anything beyond basics on your E2 request you have to get with a company chief or YN before you go and ask them to help you make the proper requests and calculations. It is complicated especially for kids who are new to GOV travel.
Bottom line: There are lots of options to do travel, but you must get expert help before you begin. The situation is, at USCGA orders always run late as there are like 3 YN for 1100 cadets who need orders, and E2 is always a rush job to get tickets etc. Often, E2 must be done within hours of getting orders and this rushing causes both errors and cadets not requesting all they are due. They give you an hour or two class on E2 and travel vouchers, but it is way more complicated than that. Over time you will figure it out as you travel more in the USCG. Find a Chief or YN that is good at travel and try to learn this early as you will then make sure you are getting reimbursed for everything you should be. For example, often cadets enter hotel and leave out hotel tax on their E2 request which can add up to a lot of money they should have been reimbursed for on a trip.
Finally, don't try to game the travel process or E2, or for that matter your PCS move to your first assignment. Put in everything you are due, but don't lie and make stuff up. Keep all receipts and turn them in even if not required for a small expense. E2 travel voucher submissions are signed under penalty of perjury and there are big penalties for cheating. Best to treat travel like taxes to the IRS, be accurate, claim all you can, but do not cheat. To many members get in trouble for falsifying vouchers.