Okay, imagine you have a group of friends who really love playing tag. They all agree to follow certain rules when they play like, "no pushing" and "only tag people who are playing." This group of friends is like Somalia, a country in Africa, and their rules are like their customs and traditions.
Now, let's say that some people from outside of the friend group come in and start pushing and not following the rules. The friends might get upset and want to work together to kick the troublemakers out. This is kind of like when Somalia became a country in 1960 with certain rules and customs, but then other countries came in and tried to change things.
So, Somali nationalism is when the people of Somalia band together to protect their country, their rules, and their culture from outside influences. It's about being proud of their country and standing up against those who threaten their way of life.