There is nothing like something controversial that is a theme of disagreement between catholics and other denominations.
Since I was a child, I always envisioned the Holy Trinity as a glass pyramid withe different colours, that litten would light up a room magically.
Later on a cathequist friend of mine explained, due to portugueses rurality, it was easy to explain it with a turnip. Nowadays wouldn't be the same...
Today, our priest explained to our children through the comparison to a product such as tooth paste, 3 in one, which is an easier version to many of them as compared to a turnip.
The truth is: it is a hard mystery to explain and even harder to grasp it. In our heart, however, we can find an answer: God is Father, Son and Holy Spirit in one. This way He can love 3 times more, better and differently. As such, He loves us with his heart, body and soul. He connects to us, the children og God, through the "non understandable", the tangible and faith. It is Him, Him and Him, 3 in 1. Is there anything else to understand?
Going therefore, teach ye all nations: baptizing them in the name of the Father and of the Son and of the Holy Ghost. 20 Teaching them to observe all things whatsoever I have commanded you. And behold I am with you all days, even to the consummation of the world. (Mt. 28, 19-20)