"sommes" is a form of the verb "être", to be.
"nous sommes" = we are.
"sommes-nous ..." means 'are we ..' in French.
Sommes-nous .... means 'are we ...' in French.
"Nous sommes" means "we are" in English.
It means 'We are'
The French equivalent of the English word, we, is: nous.So, to say, we are, you would say, nous sommes.
Literally "Pourquoi sommes-nous parler français" reads as "why are we to speak French". If you mean "why should we / why do we have do speak French", this is: "pourquoi devons-nous parler français".
"nous sommes"
Nous sommes.
The statement should be written as follows: Nous sommes forts en chimie. It means that we are strong (in ability) in chemistry.
'are we'
où sommes-nous ?
You can say "Où sommes-nous?" in French to ask 'where are we?'.