Quick answer
Ш ш is a hard sh: tongue pulled back, lips not rounded. It never softens, whatever vowel follows.
sh
How to say it
Say “shoe”, then pull the tongue back and down. Darker and flatter than the English sh.
ши is pronounced шы
Because Ш is always hard, the letter и after it sounds like ы: маши́на is pronounced “mashýna”, жить as “zhyt”. The spelling rule forces и, but your mouth should produce the back vowel.
Ш, Щ and Ж
Ш is hard sh, Щ is a long soft sh, Ж is the voiced version of Ш. The three letters look alike by design: Щ is Ш with a tail. Ша́пка, щи, жара́ — three sounds, three letters.
Typical mistakes
Reading маши́на as “mashína” with a bright i
“mashýna”
и after ш sounds like ы.
Softening ш before и or е
Ш is always hard
The vowel letter does not change the consonant here.
Check yourself
Which word contains Ш?