Stain-Removal-101 suggests adding fabric softener during the final rinse cycle, after the clothes have been washed by the laundry detergent. Depending on the type of washing machine, the softener can be added through a dispenser on the machine, in a softener ball or manually.
Some washing machines have a specific dispenser for fabric softener that releases the softener at the appropriate time in the wash. A softener ball is filled with softener and placed into the washing machine at the beginning of the wash. It is designed to release the softener at the appropriate time in the cycle. To add fabric softener manually, pour the softener into the machine during the final rinse cycle.