These 3 verb endings can all be used when one event follows another, but what's the difference between them?
[아/어]서 can be used causally, but I'm specifically talking about when it is used to say that one event follows another.
~어/아서
When the second clause is sequentially dependent on the first clause
슈퍼에 가서 장을 본다. "I go to the supermarket and buy groceries".
~다가
~었/았다가
Some other things to note: