Where do I go through customs?

I am going to Orlando, Florida in 3 weeks. I go from Halifax, NS to Washington DC then to Orlando, and the same route going back. Where would I go through customs? What does customs consist of? I have never been on a plane since I was 11 and I've never had to switch flights so I have no idea what to do. Do I get my luggage between flights? .
Thanks!

When you arrive at the airport in Halifax go to the far end of the terminal (arrivals) take the escalator upstairs, check in and you will pre-clear US customs there.

Customs asks you what the purpose and duration of your trip is, other basic questions like when you were last in the US, etc.

When you get to Washington you will not have to go through customs again before you get on the Orlando flight but depending on the airport and terminal you arrive at and if you are changing airlines as well, you may have to exit one terminal and go to another. That may mean proceeding through security again (but not customs). The purpose of pre-clearing customs in Halifax is so that the flight is then treated the same as a domestic US flight.

Whether you have to collect your checked luggage between flights also depends on the airline carrier. If you are flying one airline all the way, then your luggage will be tagged through to your destination. If a different but associated airline (for example, Air Canada and Air Zealand, both members of the Star Alliance) they will often also tag your luggage directly through.

Returning, you will go through customs in Halifax. It will be Canadian customs, as a Canadian citizen returning the questions will be much the same.

Enjoy your vacation!

Should also mention that going to Washington the security clearance checks can be much more extensive than usual, be prepared for them to hand-check your carry-on luggage and pat you down. I had this done in Montreal the one time I travelled to Washington.

I think you'll have to go through US customs in Washington DC.You don't need to worry about your luggage as it is automatically transferred to your next flight.They'll probably check your luggage in Washington in case you have something that is illegal in the US

Generally you clear US Customs at the airport in Canada. My experience is with Vancouver but here is the steps I remember from there. After you get your boarding pass, drop off your luggage (other than any carryon) and pass through the first security check point you then proceed past the duty free store(s). Once you go by them you go through the main security check point and then through US Customs and Immigration. As, based upon the information you gave, you fly directly to the US this will be the only time you clear US Customs.

Unless you are planning a stopover in Washington then your luggage will most likely be checked trhough directly to Orlando. You would then pick it up once you get off the plane there. If you are not sure they can confirm this with you when you check your luggage at the terminal on your departure day. The only item(s) you have to bring with you are any carryon items you have. If nothing else it is a good idea to bring a change of clothing in your carryon just in case your luggage is lost. Remember that you are limited in the amount of liquid/paste/gells you can bring on a plane in your carryon luggage and in the size of the bag. If you are using a travel agent check with them for up to date regulations or check with the airline you are flying with.