For millennia, human mothers nursed their babies just fine, without reading books or going to La Leche League. They knew how to do it because they had grown up seeing it done. Since the breasts have been considered sexual objects, and breastfeeding has been quite rare, for several decades now, this form of education has been lost. Mothers now need to find opportunities to see babies nursing. Photographs are helpful.
Videos are quite a bit better than that, but seeing it in person is the best of all.
It provides opportunities to see other women nursing babies, but also helps adoptive mothers find friends who will support them and think that what they want to do is wonderful. Whether or not the adoptive mother will find specific council on adoptive nursing depends on the individual leader and other members of the local group. Most women affiliated with La Leche League do not know more than the bare basics of adoptive nursing. LLL does, however, have peer councilors, who are experienced adoptiv nursing mothers, in some areas. It is important to understand that, while some preparation of the breasts is helpful, it can be done without if necessary.