"mangez et buvez": those verbs are conjugated at 2nd person plural of imperative, so it is an order or an invitation, as Ferynn says.
for your information: 2nd person singular (re. "tu") = mange et bois; 1st person plural (re. "nous") = mangeons et buvons (let's eat and drink).
Consider that someone is sitting for lunch with you and some friends. He will say "Friends, eat and drink !" giving you the signal that you can start touching the food. Well it is the same here.