Listen and practise:

----------- -------------
burn ---------- bun
turn ----------- ton
girl ------------ gull
shirt ----------- shut ---------- shot
hurt ----------- hut ------------ hot

We don't want any burnt buns
They weren't really hurt, were they?
Make a left turn
Bert was searching for his bird

Norwegian learners' problems:

The most common mistake made by Norwegians is that they tend to round their lips when pronouncing this sound, so that it becomes similar to a long Norwegian "ø"-sound. (It is practically always followed by an "r" in writing. The only exception worth mentioning is the word colonel - ).

Variant: In most American English accents, the British English -sound has an "r-colouring" to it, which is natural because of spelling, so (bird) sounds like
.

SPELLING BOX: The is always linked to an <r> in spelling <ir>, <er>, etc.; bird, person, etc.