If you just google 'What is a clause sentence?' you come up with.
Main clauses
A main clause is complete on its own. It may be a complete sentence written with a capital letter and full stop (or ?!):
Alice saw a rabbit.
Anna is eating her favourite supper.
Finally, we arrived.
Subordinate clauses
A subordinate clause is part of a larger clause.
He burns easily if he doesn�t use sun cream.
Where is the cup of tea that you promised to make?
Everything she buys is really expensive.
The class I taught last year all did quite well.