Self-employed

Thank you so much! 

I do have some follow ups though,

1) If my net income is less than the personal amount of $15,000 why do I have to pay ? shouldn't I be getting money back in my return? 

2) When I don't claim certain expenses on my self-employment section - the amount that I payback is actually less? - it doesn't make sense. Why would that happen? Am I better off not claiming them. 

3) Here is a snapshot of my income and credits, can you explain a bit more as to what you suggest? Thank you