For an ESPP which buys stock every two weeks with each pay check, what is the first day of offering period? And is the grant date price the same as purchase date price?

Additionally, for the price I paid, should I put in 85% of share price, or the amount I paid divided by shares I received? They are slightly different (I believe due to rounding on purchase) based on my account statement. I am planning to go with the actual amount paid since that seems more accurate but want to confirm.