A complete sentence has a subject and predicate, and it can be composed of one or more clauses.
A subject + predicate + ( a group of words) can form a sentence.
“I grabbed the pen”
“You ate fish.”
More complex sentences can be made by combining independent and dependent clauses or phrases through the use of conjunctions.
I went to the park and I started running
“I went to the park” and “I started running” are independent clauses combined with the conjunction “and”