Correct use of began and begun

Correct use of began and begun...?

I have to write a paper and I have a question about the correct use of began and begun. Which one is correct?
I BEGAN by being the observer for the test administration and Nicole was the examiner.
OR
I BEGUN by being the observer for the test administration and Nicole was the examiner.
Thanks for you help!

Other Answers:

Began is correct.

the first one is correct
BEGAN
is correct
but not BEGUN
because it is past tense