Hi we have entered the U.S in April 2016 on B1 B2 and now found a job and employer is sponsoring for H-1B when can he file and can we start working?

You will likely not be eligible for H-1B unless you or the employer is cap exempt. There is an annual limit to the number of H-1B visas that can be issued each fiscal year. The cap has already been met for this upcoming fiscal year. The employer could not file a petition until April 1, 2017 for work beginning in October 2017. You can read more about H-1B at http://myattorneyusa.com/introduction-to-h1b-visas.