Cuchculan
It was all for the purpose of trading to begin with. Much of it still is. You can trade freely within the EU. Not charged anything extra. Step outside the EU and even order something for yourself and the amount you have to pay on it before they hand it over to you. When the UK does leave, those same rules will apply. I order a lot from UK sites. That will all stop when they leave the EU. Cheaper buying in the shops here. At the moment it is cheaper buying from the sites. No extra charges at all.
Some countries are poorer. But Ireland needed a hand out a few years back. Country fell apart. Even the banks were broke. So you can borrow. End up having to pay back over a long period of time. It is better to remain in the EU. Trade deals are always there. The UK wanted out, but also wanted to be still able to keep the trade deal. They were told once they leave no trade deals would happen.
Each country, for the sake of keeping this simple, gives so much to the EU pot. It might be based on how a country are doing. One doing good might give a bit more than one doing bad. The one doing good now might be doing bad some day in the future and they would give less then. So there is like a little nest egg. There when needed. Case of arriving at how much a country should get. Again some countries are doing better than other countries. So they won't need as much this time around.