A digraph is term used to describe two or more letters that make one sound. Here are some common digraphs:
CH: pronounced “ch” in cheese, inches, church
SH: pronounced “sh” in shoe, mission, wish
WH: pronounced “w” in when, where, why
TH: pronounced “th” in this, weather, with
PH: pronounced “f” in photo, hyphen, autograph
TCH: pronounced “ch: in itch, catch, stretch
WR: pronounced “r”: write, wrong, wrench