How to create calculation previous month sales i need every month 1st &2nd & 15th &16th. current month 1st to till date.

Well, since that's just the same image as in your question, a little more clarification might have helped, but I'll take a guess.

DATEPART('day',[Order Date1]) IN (1,2,15,16)
OR 
DATETRUNC('month',[Order Date1]) = DATETRUNC('month',TODAY())