Hardly

We use hardly meaning 'not very much' or 'minimally':

• I am so tired I can hardly concentrate. (my concentration is minimal)
• I can hardly see anything without my glasses. (I can't see much)

Hardly is used as a negative word, so the verb cannot be negative:

• I can hardly understand. I can't hardly understand

Almost

We use almost to say something is very close to being something else:

• I exercise almost every day. (not every day, but very close to it)
• Susan is almost 6 foot tall. (she is not 6 feet, but very close to it)
• The building is almost finished. (it is very close to being finished)

Just

We can use just meaning 'exactly':

• That is just what we need now. (exactly what we need)
• The new manager is just as arrogant as the previous one.
• We are putting the finishing touches to make the party just perfect.