do we get paid if some 1 comments in our discussion

yes you get, but not much, just a small % of the worth of each reply. However you can increase the amount by giving a + or - rating to everyone, and choosing a best response.

Yes, you are paid for all your responses to your discussions, not for your comments back to your own discussions (though is important to reply back since it's a polite way to do and it keeps your discussion active). The amount earned it's secret, no one but myLot staff knows the exact sum and they're not going to reveal it. Just keep up the good work and the results will eventually show!