There are 7 digraphs that can be used to start a spelling program; ch, sh, th (thing), th (this), wh, ng, and nk. The first thing to do is to associate these digraphs with commonly used words with the child. To assign a sound with a digraph, use flash cards for better association for the child. You can buy these cards at any teacher supply store or you can make the cards yourself. Before making the cards, make a list of words for each digraph. Here are some examples of words you can use:
CH (beginning with):
choice, chop, chips, chew, cheer, chase, chain, chalk
CH (ending with):
coach, beach, teach, each, reach, ouch, touch
SH (beginning with):
shine, shop, shell, shout, shade, shower, share, shut
SH (ending with):
wash, fish, dish, rash, push, rush, slush, mesh
TH (as in thing):
thing, these, there, they, the, then, them, their
TH (as in this):
this, theft, thumb, with, truth, thank, thick, thin
WH:
when, why, where, what, white, while, whistle
NG:
ring, sing, thing, ting, challenge, change, rang, sang
RK:
rink, sink, mink, think, rank, thank, link, dink
You can always add more words to the list. A good tip is to add words that are familiar to your child. For instance, if your child have a favorite toy, food, or friend whose name sounds like one of the digraphs, use it. It will better help the child associate the sound to the other words in the list.