My mother takes great care of all the members of the family. She manages the family well. She has a good sense of sanitation. She keeps our house neat and clean. She is an ideal woman. The first sentence of the above passage is a principal clause because it has a subject My mother and a finite verb takes and it gives a complete sense. Similarly, the other sentences in the passage also give a complete sense. So they are simple sentences.
The clause which contains one subject and one finite verb is called an Independent or Principal or Main clause. It gives a complete sense. It can stand by itself as a sentence even if it is part of a larger sentence. There is a similarity between a simple sentence and a principal clause.