Digraphs are consonants that combine in English to make a single distinct sound:
On the left side of the keyboard:
TH-: This is used for the 'th' sound.
KH-: This is used for the 'ch' sound.
SH-: This is used for the 'sh' sound.
On the right side of the keyboard:
*T: This is used for the 'th' sound.
-FP: This is used for the 'ch' sound.
-RB: This is used for the 'sh' sound.
-PBG: This is used for the 'ng' sound and the 'nj' sound.
Notice that there is no way to produce the 'ng' or 'nj' sounds on the left side of the keyboard. This is because in English, virtually no words begin with those sounds. And any few that you may encounter are easily dealt with via briefs.