The "es" and "est" are conjugations of the irregular verb être (to be).
Je suis = 1st person singular = I am
Tu es = 2nd person singular = You are
Il/Elle/On est = 3rd person singular = He/She/One is
Nous sommes = 1st person plural = We are
Vous êtes = 2nd person plural = You are
Ils/Elles sont = 3rd person plural = They (masc.)/They (fem.)
And, yes, "le" is for singular masculine nouns and "la" is for singular feminine nouns
"Oui" is pronounced like "wee." I'm not sure if it is a regional thing, but keep in mind that DL is capable of messing up. I personally didn't have a problem with the audio, but that doesn't mean it didn't mess up for you.
(Sometimes it takes a little while for people to actually understand the audio, so if you want to be sure your answer is right, listen to the slow audio (if available, of course) because the DL team usually gets them right)