This adverb has negative connotations already so is not used with "some" or "never", for example, but with "any" or "ever":

I hardly ever see John these days. (I almost never see him.)
I have hardly any money on me. (I have almost no money in my pocket.)

It is similarly used with anybody, anyone, anywhere, anything.

The boss knows hardly anything about the production line.
Hardly anybody in the company speaks English.

Uses without any etc.:
Mary hardly spoke during the entire meeting. (She said very little.)
It was so dark I could hardly see where I was going. (I could see very little of what was in front of me.)
Speak up! I can hardly hear you. We have a bad connection.

Notice the position with compound tenses:
I have hardly started the job. I still have a lot to learn.


With the past perfect tense there are two possibilities:
He had hardly put the phone down when it rang again.
Hardly had he put the phone down when it rang again.
The second of these might be considered more formal or literary.

Short answers:
In answer to a question "Hardly", "Hardly any" etc are often used alone:
"Do you believe in ghosts?" - "Hardly!" (an ironic understatement)
"How much money do you have on you?" - "Hardly any."
"So who do you know at this party?" - "hardly anybody I'm afraid"