How do you configure turbo to calculate straight line depreciation?

What are you trying to depreciate ?   How many years ? 

buildings are automatically straight line.  for to add other other assets using straight line you need to select intangibles, other property

then select other asset type next window

next window select asset class - note using straight line requires using the ADS recovery period - see iRS pub 946  table b-2

then on next window select straight-line

You should not have to "configure" anything to use any type of depreciation. The program does it automatically for you. But for every rule, there is an exception. So just exactly what is it you're trying to depreciate?