Songun is a big word that means putting military stuff first in a country. In simpler terms, it basically means when a country focuses more on its military than on anything else.
Basically, the government of a country that practices Songun gives more attention to their soldiers, weapons, and defense than to anything else. This means they spend a lot of money on their military instead of on fancy buildings, roads, schools, or hospitals.
It's like when you have a bunch of toys but you like one toy the most, so you spend all your time playing with it and you forget about the other toys. In the same way, these countries spend most of their money and resources on the military and sometimes forget about other important things like making sure everyone has enough food and water.
Some people like Songun because they believe that it helps protect their country from other countries that might want to fight them. Other people don't like it because they believe that it's not fair to spend so much money on the military when there are so many other important things that need funding.