What makes a complete sentence?
If it helps you, think about a sentence as if it were a skeleton, the skeleton contains various bones and these bones are put together to form different parts of the body. So are sentences formed by words, the words are the bones and they are put together in different ways to form sentences.
But just because you put words together in the right order, it doesn't mean you will have a sentence that makes sense.
Try this fun sentence generator (it's a computer programme, so there may be some issues. What the heck, it's clever stuff - see if you can spot them