According to expression, sentences are of four types. They are:
Declarative sentences/Assertive sentences: These sentences make statements. They can be affirmative (positive) or negative. They end with full-stops (Periods in American English)
They sell all kinds of vegetables.
We are not interested in playing games.
Interrogative sentences: They ask questions. They end with question marks. (?)
What are you doing in the garden?
Where is John now?
Imperative sentences; These sentences give commands, instructions, etc. They usually end with full-stops. Sometimes, they end with an exclamation marks when they are strong.
Come and sit here.
Shut your mouth!
Exclamatory sentences: These sentences express sudden feelings and emotions. They end with exclamation marks.
What a lovely garden this is!
I love this shirt!