What should you do first to write 5.871x10-7 in standard form'

Well first you look at the exponent with 10. This is - 7. This tells you to things. The negative tells you that you will be moving the decimal place to the left and the number 7 tells you how many times.

5.871

Shift for the first time

.5871

Shift for the second time

.05871

Shift for the third time

.005871

Shift for the fourth time

.0005871

Shift for the fifth time

.00005871

Shift for the sixth time

.000005871

Shift for the seventh time

.0000005871