Ganden Phodrang is a very fancy way of saying "government." It was the official government system of Tibet, which is a place far away that has mountains and lots of people who practice a religion called Buddhism.
In the olden days, Tibet was ruled by a king who was also a religious leader. But then, a long time ago, a really smart man named Tsongkhapa came along and started a new type of Buddhism called Gelugpa. People really liked this new type of Buddhism and it became very popular, especially with the king.
So, the king decided to make the Gelugpa the official religion of Tibet and he put Tsongkhapa in charge of the government. This was the beginning of the Ganden Phodrang system. It basically meant that the religious leader was also the political leader.
Over time, the Ganden Phodrang system became more complex and there were different levels of government officials who helped run things. The people who worked in the government wore special hats and clothing to show that they were important.
But then, something sad happened. A country called China decided that they wanted to take over Tibet and make it part of their own country. The Tibetan people didn't like this, and they fought back, but they couldn't win.
So, now China is in charge of Tibet and the Ganden Phodrang system is no longer in place. But, some people still remember it and think it was an important part of their history.