When two or three letters are said together and we can hear each sound, then it is a blend. Blends are also called Clusters. Note that vowel sounds are not heard in a blend.
Now, blends can occur at the beginning, middle or end of a word.
Consonant Digraphs
When two consonant letters say one sound, they are called digraphs.
Now in a blend you can hear each sound but in a digraph you only hear one sound. Digraphs are represented by a phonetic symbols while blends are not.
Examples
Blends:
Sm, sp, br, ft, cr, sl, tr, tw, etc. When you pronounce any of these, you can hear both sounds in each blend.
Sm – smile, smart
Sp – spark, spray
Br – brow, bread
Tw – twin, twist
Tr – tray, trip
Cr – crest, crystal
Ft – left, craft
Digraphs:
Th, sh, ch, ck, ph, kn, etc. When you say any of these digraphs you will hear only one sound.
Th – thin, teeth
Sh – ship, dish
Ck – crack, shack
Kn – know, knee
Ph – photo, physical