the TPO (Postal Wagon) postmark is from line 21-22, i.e Kiev to Odessa.
The date of posting is the 5th of May, 1873. The month is given in the second line of the date, in words. The first line of the date has 2 numbers: a "16" and a "5". The "5" refers to the month (May), while the "16" refers to to the number of the railway station along the route at which the piece of mail was collected.