Buvez-en!  Here en refers to a part of a group or quantity (remember, en replaces de+noun). Drink them would be buvez-les.

J'ai encore du lait dans le frigo. Buvez-en. -- I have more milk in the fridge. Drink some (of it).
Vous trouverez deux verres avec du lait sur la table. Buvez-les. -- You'll find two glasses with milk on the table. Drink them.

Qu'il y en a un sur deux qui n'est jamais  heureux. -- That there is one in two who is never happy.

When you want to express that there is a certain number of something, you use il y en a...

Je dois acheter du lait? -- Non, il y en a encore un litre.
Combien de plats sont sur la table? -- Il y en a quatre.

Thank you so much, Chris! I understood everything about this sentence but the usage of en. Now it all makes perfect sense.  

Bonjour Allison, Comme l'exemple, soyez prudente. You are correct that etre uses le subjonctif in the imperative. Let me say, that, like yourself, I am but a Kwiziq community member, i.e. a member of the group, and not part of the Kwiziq team. I love the French language and have studied it for many years but still have a lot to learn. This being an open forum, I simply try to answer questions that I have an educated response for. So to that end, I have never run across in my studying or reading anything that explains the reasoning for the use of le subjonctif for etre in the imperative. I will, therefore, leave this question to Aurélie or another Kwiziq team member to provide you with the correct response. Bonne chance et bonne continuation dans vos études en français.

Yes Laura that does make sense but still left me with questions until I clicked on the link for imperative

Bonjour Jacqui, «take him two» is the translation for «prends-lui deux». If possible, could you include the question that you are referencing on this and resubmit it à bientôt

The lesson concerning «lui» in affirmative commands follows: Le, la, les vs lui, leur in affirmative commands (L'Impératif) I am unsure if this is the lesson you are referencing or not; however, let's look at this example. Ah, les bonbons. Prends-lui deux. This scenario could be two friends talking and the one with the bonbons tells the other to take two to her brother, whom she knows.

Bonjour Ron. Thanks for the clear answer. À bientôt, Jacqui

Bonjour Steven, Below are the imperative forms for avoir: Impératif Présent aie ayons ayez While the present participle and gerund are: Participe Présent ayant Gérondif Présent en ayant As can be seen, these forms are based on the subjunctive.

Hi again, Your question actually prompted my own: Why is the subjunctive Nous form used to make the present participle with the verb avoir when the majority of other verbs do not, they use the nous form of the present tense? However, être uses the nous form of the imparfait to form the present participle.