Hey there!
"Let alone" is sort of an an idiomatic phrase and you use it for emphasis when comparing two things. Usually the second thing is bigger, or more important than the first. ...At least, that's how I use it!
Merriam Webster defines it as "to say nothing of" or "not to mention."
You're should be safe using it like this:
"let alone" + infinitive
or
"let alone" + article + noun
Ex.
"Very few people ever meet a senator, let alone a president."
"I don't have enough money to buy a new TV, let alone a flatscreen."
And this one I just found on the web which made me laugh: "I can't remember what I had for breakfast yesterday, let alone the plot details of Pride and Prejudice, which I read back when I was in high school."