Here are some paragraphs to help you to get the story:
I can’t tell you how good it made me feel to see them so bright and
cheerful. Our life wasn’t easy. The Dooley family was never generous
to my father. They owned the Dooley Brothers Ranch, the big riding
stable in North Hills. As a teenager, Dad had worked there as a stable
boy. He returned to the stable after two years at a community college.
Eventually, he worked his way up to assistant manager. But the Dooleys
ran the place as if they were kings and he was their servant. They
never let him forget that he started out with a shovel in his
hand. Martin Dooley, the stable owner, was always reminding Dad how
grateful he should be, how he’d be nothing without the Dooleys’
My question is whether this sentence is an idiom or I just need to translate it directly.
And I also don’t know the meaning of this idiom:
Stick out my jaw
In the U.K., a shovel is a particular tool, used by unskilled and until recent times casual labourers on building projects of all kinds, including railway construction, and the digging of the canals that preceded them. A shovel looks like this: https://media.gettyimages.com/photos/garden-spade-picture-id185074028?s=612×612. I myself used one as an undergraduate, earning money during university vacations. Unlike a flattish spade, It’s concave surface is ideal for moving large quantities of material from one place to another.
The casualised and the physically exhausting and unskilled nature this work made it and the worker themselves despised by many of the middle and upper classes.
So here the passage makes it clear that we have someone who has managed to rise from the labouring class into a respected middle class profession. But, instead of being admired for the effort and success, people see him as an upstart and keep reminding him of his humble origins: born with a shovel in his hand. This is typical British snobbery. You could call the expression an idiom of its day. But it and the shovel have rather been displaced by the mechanical or hydraulic digger!