Difficult is the opposite of easy. It means that something requires lots of effort to do it. Hard can be the opposite of "soft" (such as a hard pillow and a soft pillow) but it can also mean "difficult."
For example, you can say:
The test was difficult. = The test was hard.
It's difficult to understand the teacher. = It's hard to understand the teacher.
The word hard is a little more informal, so it's better to use difficult in more formal writing.
The word hard can also be an adverb to describe doing an action with great effort or energy. We often use it with the verbs work and try:
Adding extra eye fringe amps up the glam instantly. First, take your falsies and loosen them by gently flexing the eyelash band, then curl your natural lashes to make sure your falsies line up with your actual lash line. Apply glue on your falsies using a Q tip. Using tweezers (or finger tips if you feel that gives you more control), place your falsies as close to your lash line as possible. Let your lashes dry for a minute before you add a coat of mascara (this is optional).