Hi, I was wondering if someone could help me with the construction of the H2S MO?

I know that the 1s orbital of H spans the a1 and b1 irrep, the 3s and 3pz of S span a1 only. 3py spans b2 and 3px spans b1. a1 and b1 will be bonding, and b2 non-bonding. However, I'm not really sure about how to put all of this together, the only example I have been able to find is of H2O, but I don't understand the diagram.

Thanks