The word ‘sentence’, in general sense, has these dictionary meanings: ‘the punishment given to a person by a court of law’, ‘to say officially in a court of law that a person is to get a particular punishment’, but in English grammar:
“A sentence is a group of words which has a subject (one or more) and a predicate (one or more), and gives complete sense.”
When we write a sentence, we must begin it with a Capital Letter and end it with either a full stop [.] or a question mark [?] or an exclamation mark [!] depending on the context.
Stop. [= You stop.]
He is a boy.
She goes to school and (she) studies very hard.
I returned home early because I was tired.
Do you like this book?
What a beautiful garden it is!
The six groups of words given above are six complete sentences.
A sentence must have a Subject part and a Predicate part: a subject part must have a noun or pronoun; a predicate part must have a main verb.
e.g. Our children are playing in the park.
‘Our children’ — subject part — children – noun
‘are playing’ — predicate part — are playing – main verb