Hi esroa, and welcome to Using English.
Hardly is an adverb, but in the form of English I use, it's not the adverb form for hard.
Hard is both the adjective and the adverb form.
You need a hard surface to work on.
I hit it hard. -- I would never say "I hit it hardly."
Hardly, as I use it, is used to show how the small amount of something or how minimal it is.
There is hardly any milk left. I hardly touched it.
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