what is the difference between stop and start database?

Hello everyone,

I have one question about the stop/start database.

I have read the Oracle document about stopping and starting the database:

However, I really don't understand so much and hope for an explanation from you guys.

When I check the Database Properties after daily maintenance, I always see that all my database under the application was stopped.

Why, after running daily maintenance, are they always stopped?

Thanks and have a nice day!!!