are
The word 'sont' is the French equivalent of the English word 'are'. It is used to express the plural form of the verb 'to be' in the present tense. For example, 'Ils sont grands' translates to 'They are tall' in English.
They are very intelligent.
In this sentence, 'sont' is the third person plural present form of the verb 'être' (to be). It is used to describe a characteristic of a group of people or things, in this case, to indicate that they are intelligent.
The flowers are beautiful.
Just as with the prior example, 'sont' here is the third person plural present tense of 'être'. It is used to describe a plural subject (the flowers), indicating that they possess a certain quality or characteristic, in this case, beauty.
Where are the keys?
In this sentence, 'sont' stands for 'are' and is used as part of a question inquiring about the location of an item or items (the keys). It is once again a form of the verb 'être', used here in the context of figuring out where something is.