What are the ten courses of action (kamma)?
1. What are the ten courses of action &amp; their significance?

They are unwholesome and wholesome behaviors that lead people to live unhappily or happily now &amp; in the future.  

Unwholesome Course
Bodily Conduct
1. Killing &amp; harming living beings.
2. Taking what is not given.
3. Sexual misconduct.
Verbal Conduct
4. Lying.
5. Slandering.
6. Harsh talk.
7. Useless Idle chattering.
Mental Conduct
8. Covetous thinking.
9. Hateful thinking.
10. Seeing distortedly with wrong view.  

Wholesome Course
Bodily Conduct
1. Abandoning killing &amp; harming living beings.
2. Abandoning taking what is not given.
3. Abandoning sexual misconduct.
Verbal Conduct
4. Abandoning lying.
5. Abandoning slandering.
6. Abandoning harsh talk.
7. Abandoning useless idle chattering.
Mental Conduct
8. Abandoning covetous thinking.
9. Abandoning hateful thinking.
10. Seeing undistortedly with right view.
(You can find details about them in the references provided below.)  

2. What are their references?

You can find them in many discourses throughout the Pāḷi Canon, specially in the 10th book of the Numerical Discourses (Aṅguttara Nikāya).  

Two examples are: AN 10.176, Cunda (Cunda-suttaṃ) &amp; MN 41, Brahmans of Sala (Sāleyyaka-suttaṃ).