Hola Stephanie

The gerund/present participle is used in different situations. We use it with estar when we are forming a progressive tense: I am doing something, she was doing somehing, they will be doing something, etc. See this lesson for example on how to form the present continuous/progressive tense. 

But there are also other ways to use the gerund/present participle, like the one showed in that lesson for "to say by doing something". 

I hope it clarified it for you.

Saludos cordiales

Inma