Relactation or induced lactation (for those who did not give birth to their baby) is essentially a two-fold process:
You will be teaching (or re-teaching) baby to nurse at the breast, and to equate nursing with comfort. If you’re having problems getting baby to nurse, see Help — My Baby Won’t Nurse!
At the same time you will be developing (or re-developing) a milk supply. Developing a milk supply requires nipple stimulation (via baby nursing, hand expression, pumping or a combination) and milk removal (once there is milk to remove). If your baby will nurse, regular and frequent nursing sessions (even if baby is just learning in the beginning) will be very helpful.