"To fire a rifle you have to pull the trigger"

It can be used when someone makes a decision or does something. E.g. "The game I want is on sale. Should I pull the trigger?", "He pulled the trigger on the deal." etc.

The urban dictionary lists meanings that are not used in public. People read about words used in ways defined by the urban dictionary and then they know why they should avoid using words in these ways.

it is up to you. I doubt that "pull the trigger" sounds very urban )

I doubt that anyone on italki would write any of the meanings in the urban dictionary. I refuse to write any of them.