The Norwegian National Treasury is like a big piggy bank that belongs to the country of Norway. The people in charge of this piggy bank, called the Norwegian government, decided to send some of its money overseas to different countries. But they didn't want to just give the money away, they wanted to make sure it would grow and become even more money for the country in the future.
They decided to invest the money in different things like stocks, bonds, and even other countries' currencies. They did this because they thought these things would become more valuable over time, kind of like how you save your allowance in a piggy bank and hope it will grow bigger.
When they invested the money, they had to fly it to these other countries, which is called the "flight of the Norwegian National Treasury". But instead of using an actual plane, they use a system called electronic funds transfer to send the money from the Norwegian piggy bank to the other country's piggy bank.
The Norwegian government is very careful with their money and tries to make good decisions with it, so that in the future they will have even more money to spend on things for the people who live in Norway.