"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'
We are here.
You can say "Nous sommes arrivés" in French to mean "We've Arrived."
"we are ready" is "nous sommes prêts" ("prêtes" if it is an all-girl group) in French.
You can say "nous sommes à la maison" in French to mean "we're home."
You can say "Où sommes-nous?" in French to ask 'where are we?'.
"We are alike" in French is "Nous sommes semblables."
"We are called" in French can be translated to "nous sommes appelés."
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".