I cleaned the windows. I cleaned them myself. I had the windows cleaned. I arranged for somebody else to do it. I got/I had - both work the same way.

"I got" and "I had" are not the same. "I had the windows cleaned" means someone else cleaned them for me. "I got the windows cleaned" can mean the same, but it might not. It can also mean that I cleaned them myself. It can mean I purchased or found the windows and they had already been cleaned when I bought or found them. The verb "to get" is like a chameleon that changes its meaning to whatever the speaker wants it to mean. More than most words, its meaning depends on context. For that reason, it should not be used in situations where you need to be understood. It is fine to use "get" in well worn phrases like "they get along" or "let's get going". I don't know why "they get along" means what it does. It just does. Learn such phrases and use them without puzzling why they mean what they do. Other than that, just use "get" when you can't think of a better word.