can someone tells me what is .First ?

Question

Hi experts,

 

 

I have this rather stupid question yet I duno the answer.  Hope someone can let me know the answer :

 

public AzolaDL.Account getAccount(string userName, string type){
AzolaDL.Account account = new AzolaDL.Account();
try{
     account = db.Accounts.First(e => e.userName == userName && e.type == type);
}catch (Exception e){
return null;
}
return account;
}

 Can I know why do we need to put .First ?