There are different ways and situation in which you'd use an -ing form: Use to be + verb + -ing for the continuous. For example with verbs. You are then dealing with the Continuous.
When the -ing form occurs as a noun, we call that 'gerund'.
Below you'll find three ways in which a Gerund occurs:
A Gerund can occur as subject:
Parking is not allowed here.
Smoking is bad for you health.
Flying is not dangerous at all.
The Gerund is used after a number of verbs, when people speak of general (non-specific) things.:
He really likes running.
I enjoy travelling.
Stop lying to me!
The gerund is used after all prepositions:
Before going home, you must have a look at my new computer.