3 Answers

Explanation from one Biblical scholar here.....

http://www.clarifyingchristianity.com/trinity.shtml

I explain it this way. Water + sugar + flavoring = koolaid. 

How do you explain it? 

Serious answer.....as I see it,

The Father = the IT, the creator

The Son = the human man sent to spread a message of God's love and infinite wisdom. 

The Holy Spirit is the essence of "God", it is the love, light and sound of God. Something that all Souls contain. 

The Catholic religion explains it in their own way. Catholics have been known to argue with each other in the proper way to explain it. It's still like a mystery because no matter how it gets explained, it still seems confusing because they are trying to take two separate entities and make them one. 

Best to ask a Jehovah's Witness or a Muslim.