I never know when to use etre and avoir. How interchangeable are they?

So, etre and avoir are the two most common French verbs so it's really important that you know when to use them. First of all, we will make sure that you know how to conjugate them in different tenses. Etre means 'to be' and avoir means 'to have'. However, they are both used as 'auxilieres' in the 'passe compose'. In this past tense, let's say that 80% of the time we will use avoir. But there are some exceptions. A way to remember them is to call them the DR MRS VANDERTRAMP words because the verbs that take 'etre' are 16 verbs that start with those initials!