Gerund/base form

Hi,guys.I'm here to ask something about gerund.Well, just now when I loged onto an english-learning website.I came across a logo which says "Having english grammar troubles?Well no one said it was logical.Just try it and go on."

When asking questions.I seldom saw people beginning their sayings by using "verb+ing" form. Base form of verb is preferred. so, Why must use gerunds? and how I know when to use base form and when to use ing-form as in this case?

"Having" is not a gerund. It is a shortened form of a present progressive, as is common in spoken English. Written in full it would be:
"[Are you] having English grammar troubles?"

thanks a lot!