Entropy is the a count of how many ways you can rearrange the insides of a thing while keeping its external state unchanged.
Sometimes we talk about arrangements of molecules, in a gaz or a liquid for example. Sometimes we talk about arrangements of energy packets, when heating a solid for example.
By adding more packets, for example adding more air inside of a baloon or making a pipe hotter we increase the entropy.
We can also increase the entropy by spreading the packets into larger areas, when connecting 2 pipes for example. In that case the amount of enery in the 2 pipes system stays the same but energy packets have more arrangement slots.
There are simply more ways to spread packets around than to keep them confined so increasing entropy is more likely. For example, given an amount of sand, the arrangements of grains that would make a castle are a tiny portion of all possible arrangements.
The 2nd law of thermodynamics states that in an isolated system entropy can only increase, meaning that our universe is slowly going toward a cold equilibrium at maximal entropy.
Put another way, things don't grow organized/useful by themeselves. They need external energy for that.