Indeed, they are two separate concepts.

I write lots of automated tests, but almost always after the development is finished. The only exception is when reproducing a bug, where I first write the test that reproduces it, then I fix the code.

TDD is about developing tests first then writing the code to make the tests pass. I know several people who gave it an honest try but gave up a few months later. They do advocate everyone should try the approach, though, simply because it will make you write production code that's easier to test later on.